Welcome to the forum. The picture shown by you looks just like a standard German silver hallmark of that time (mid 1880s onwards) and has nothing to do with the watch per se. So, the case is German (not unusual at that time, even in Swiss watches).
The 0800 is the silver content (80% pure silver, which is a sometimes referred to as coin silver). Thats a "usable" silver content (as opposed to the higher grade Sterling standard of 95%). Coin silver doesn't polish as brightly as sterling, but it's more rugged and doesn't tarnish as quickly, usually. If the other code looks like it was hand written, then yes that's a watchmakers service code. Generally useless to you unless you happen to have access to the original watchmaker's records.
The blue numbers on the dial and general design of the watch point to the 20's, I think. It's a pin-set movement (you set the time by pushing in the pin to the right of the crown, then turning the crown). This type of system was decreasingly common after the turn of the century, and could suggest a somewhat more functional, lower-grade movement. That would be in keeping with a watch being sold in Germany post WWI, but I'm speculating a bit. We'd need to see a picture of the movement (the part with the gears) to say much more.
Resolved, it UOT.
Tellus (Ulrich Wilhelm) - founded in 1928 in Frankfurt. Tellus brand was registered on 22 February 1927 in Switzerland. The most famous watch brand was UOT. In 1939 the company was in liquidation.
Is this correct?
You are right with "Uhr ohne Tadel" and I want to add its german and the translation would be "watch blameless". I like this . Later on you often find cortebert movements inside but in this case I think Hartmit is right.
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