Thank, you Fritz, for your note and information. Of course, we can not know for sure, and all information is useful. I would like to provide more information, though, in the context of your note for the benefit of general knowledge. My intent is neither to refute or argue. Your surmise (as I explain below) is also valid. My thinking in doing this reply is that this thread is an opportunity to post more information in general on the topic of German swords and their markings, and my research on this sword involving how the interplay of history and physical evidence can inform our understanding. Let's begin with what is evident, and then go on to what is nonstandard (leading to assumptions):
1. EVIDENT PHYSICAL TRAITS:
SWORD ORIGINS AND DATE: The blade style and hilt are consistent with all sources (that I've seen) for the M1852 Cavalry Saber. The blade markings are consistent with markings for the Prussian Army of that period, both the acceptance markings on the spine and the manufacturer on the ricasso. The Depot marks on the blade and the hilt all match, and are also in the form consistent with the sources on Prussian weapon markings of the period (and the blade). Given all of these points, I think it is more likely than not that this is as it seems: an M1852 Prussian Cavalry Saber that was accepted into the Prussian Army inventory in 1856. There is nothing among these markings or elsewhere that would suggest otherwise. Of course, there is no telling what the sword's history was after that, or where it may have wound up--which does not rule out Fritz's surmise that the unit markings are post WWI and not Imperial German. I accept that possibility.
2. EVIDENT HISTORICAL RECORD:
THE REGIMENTAL HISTORY (WEST PRUSSIAN UHLAN REGIMENT #1) PRE AND POST BLADE DATE (1856): Fritz's reference and comment suggests that the unit in question did not carry the name (West Prussian) until sometime after 1856: "The unit that eventually became known as Ulanen-Regiment Kaiser Alexander III von Rußland (Westpreußisches) Nr. 1" (I may not be correctly interpreting the suggestion, though). Even so, I don't think that this would rule out that this weapon could have been assigned to that unit: it could have been accepted into service in 1856 (as its markings show) and issued from the depot a later date at which time it would have received the unit stamp. Setting this question aside, I believe that the preponderence of information indicates that Prussian Uhlan Regiment #1, with the designation "West Prussian," was within the standard naming convention for this unit before and after 1856 (up to and including World War I). Every order of battle or unit list I've seen includes the regional designations along with regimental numbers, and it does so in the case of this unit within them. Here are few examples:
PRE 1856:
Unit Formation:
I'm not sure if this will expand to be read-able, but to summarize, Prussian Uhlan Regiment #1, with the designation "West Prussian," was formed in 1808. I believe this also addresses Fritz's source's mention of Silesian Uhlan Regiment #2.
Found in: Nafziger, George (1996). The Prussian Army, 1792-1815, Volume III, The Cavalry and Artillery. Nafziger ISBN 1-58454-017-0
Prussian Order of Battle, Waterloo Campaign:
The unit is listed as "1st Westprussian Uhlanen Regiment" in the 1st Brigade, IV Corps Cavalry Division
Found in:
Order of Battle in The Waterloo Campaign Wikimedia I recognize that Wikimedia is not necessarily definitive; however, I refer to it as a representative example from the era. The naming convention for every Prussian OOB that I've seen for this era includes unit regional designations, to include the "West Prussian" designation for Uhlan Regeiment #1.
POST 1856:
1866 Campaign:
"Prussian 10th Division, V Corps:
“'West Prussian Uhlan Regiment Nr. 1'”
Given that this unit list was compiled for a text published in 1870 (see citation), it demonstrates naming conventions that are just about contemporary with events--as opposed to later lists which may be adding designations based on later naming conventions.
Found in: Fontane, Theodor (1870), The German War of 1866: The Bohemian and Moravian Campaign. Helion (2021, Trans. Frederick Steinhardt) ISBN 978-1-914059-29-2 [Unabridged, tranlsation of Fontane’s Der deutsche Krieg von 1866, Vol 2, published in 1870)] Page 190
Again, I'm not sure if the above will expand to be readable, but I thought I would include it. This is the entry showing "Westpreussen Ulanen Regiment Nr 1" (uniform for 1866) in the Sturm Cigarette card book on German Uniforms during the "Age of German Unification 1864-1914," published in 1933 (found on page 13 among the other Uhlan Regiments). Again, not definitive in itself, but consistent with other points of information.
2. NONSTANDARD TRAITS: ASSUMPTIONS AND GUESSES (THE UNIT MARKINGS):
It would be nice if the markings on this sword conformed to the exact specifications of Prussian unit markings in terms of placement, sequences, font sizes, and font sequences. Unfortunately, that is not the case, and I acknowledge that as well. And I certainly can't say for sure what the unit designation is. However, I think that the record shows that the unit stamp on this sword is not beyond the range of the local variations compared to other Prussian/German Imperial swords.
Comparison of Unit Stamp Examples:
The below images are from this reference: Hughes, Gordon A.(1975) A Compendium of British and German Regimental Markings: Compiled and Edited by Gordon Hughes and Chris Fox. Benedict Press. (I hope that the scans expand for reading).
Uhlan Vs Non-Uhlan Stamps
In the above left scan, I have put together the stamps for all the Uhlan regiments found in Hughes (Note that the "R" indicates an italic R indicating Reserve). In the above right, I have put together all the other stamps that have a "U" in them: these are non-uhlan units. It is clear that there is a variance in format between the Uhlan regimental stamps and the others (which do not conform to the same format). Although not exact, the sequence of the unit stamp on this sword (1. W. U. 5. 50) is more consistent (the addition of the "W" being the outrider) with the uhlan regimental stamps (example: 12. U. 3. 110) than the non-uhlan examples. This in itself is not definitive, I certainly recognize, but it is one point.
Example of Unit Stamp With Regional Designation Letter Included:
There is an example in Hughes of a unit stamp, 1. O. R. 3. 25 (3rd Company of the 1st Ostasiatisches Infanterie-Regt. Weapond 25), that is in the same format and sequence as the unit stamp on this sword. Again, a this is different kind of unit, and not in itself proof of anything, but it does show a precedent for the kind of unit stamp found on this sword--and is another point of information.
Examples of "Nonstandard" Unit Stamp Variations Found On Other Swords:
I don't have permission, so won't post a shot of the images shown there, but in that post, Uhlan shows an example of an 1852 Cavalry Saber identified as belonging to the 3rd Squadron, 10th Uhlan Regiment. The unit stamp on that sword is "nonstandard": U. 10. 3. 90 (compare to Hughes: the regimental number should come first, followed by the "U").
Nonstandard Hussar Unit Stamp
The above is the unit Stamp for a Prussian Hussar Regiment found in Hughes: 3. H. 5. 75 (5th Eskadron of Husaren-Regt. Nr 3, Wpn 75).
In
Pin & Sword's Youtube Video on the Prussian M1852 Cavalry Saber, one of his sabers is identified as a hussar sword. Again, I don't have permission to use the images, but the unit stamp on that sword is "nonstandard":
H. R. 16. 1. E. 2. (1st Squadron, 16th Hussar Regiment, Weapon #2). Again, like the Uhlan Stamp in the Above example, this unit stamp is technically out of sequence, and the addition of "E" for the squadron is also technically nonstandard. However, I have seen both the "E" and also the "H. R." on other swords. By itself, these do not directly demonstrate anything specific about the unit stamp on my sword, but they are more points of information concerning local variations of unit stamps.
OTHER NON-INFORMATION: There are no other markings of any kind on the blade or hilt. If we accept that the unit stamps are legitimate and it had a service life that began in 1856 that extended to after WWI (per Fritz's surmise), then it would most likely have more than one unit stamp (the previous units being cancelled). This is not definitely the case (of course). It could have been in depot or somewhere else for five decades and then come out after WWI and been issued to a unit in some other nation--and unit stamped--but that I think is the less likely circumstance. The sword pattern in question was also used by Spain and Argentina: I have seen examples of those, and they have markings indicating as much (this sword has none of those marks--so again, we can't rule this out, but the absence of those marks, and the presence of the Prussian ones, makes this the less likely option). The Saxons adopted this sword pattern, but the grip on this sword is clearly of the Prussian model (consistent with the unit stamps), so it is not likely that this is a Saxon sword.
SUMMARY: WHAT DOES ALL THIS ADD UP TO?
I certainly respect and appreciate the expertise and information brought to this topic by Fritz, nor do I intend to refute his conclusion. I would simply suggest that we are dealing with probabilities, and my approach would be to add up the points that are present and evident and comparisons to other swords. The main question with my sword is the nonstandard unit marking. I think that the examples show that the unit stamp on this sword is within the range of variance shown on others (obviously, this is debatable). This, combined with all the other points, though, makes it more likely than not that this sword is Prussian/Imperial German. And given the unit stamp form, it may not be conclusively stated that it was assigned to the 1st West Prussian Uhlans (circa 1856), but I believe that--at the very least--this cannot be conclusively ruled out given the variances demonstrated in the reference and in comparison to other swords. There are, of course, other ways to interpret the information, which I certainly won't refute. However, I thought I would lay out the information that I had and my methodology.
Attachments:
, but can't have everything all the time. I've yet to give it a clean, but I won't be getting it to the wonderful condition that yours are. 
