These are 1891-1939 proof marks. Crown over "U" is final definitive proof and Crown over "G" is proof for rifles. The Crown over S is final proof for the shotgun barrels and the Crown over W indicates it was proofed for choked barrels. The Crown over U on the water table likely means Suhl manufacture. What I do not see is a Crown over N which would indicate nitro proofing.
The design of this gun with a cross key forend latch and under lever action lock would indicate late 19th century production. It was a very basic gun when manufactured. None of the photos show the actual locking mechanism, but this was a classic black powder design.
Looking at the texture being hidden by whatever is coloring the barrels, I would suspect the shotgun barrels are actually twist (damascus) of some sort, and based upon the overall quality of the gun, likely not the finest. For instance, damascus barrels on a best quality English or Continental gun are often as strong as their fluid steel counterparts. This gun would be very unlikely to have such. Also, during this transition period, damascus shotgun barrels were often combined with a steel rifle barrel.
Unless there is some other evidence, I would assume this is a black powder gun (fluid steel shotgun barrels or not). Until proven by a barrel thickness gauge, I wouldn't consider firing the shotgun barrels regardless of their actual condition under whatever that is hiding them. The condition of the name and raised spots indicate to me it the barrels have seen both significant buffing and corrosion.
As noted above, I would only trust a chamber cast to know what the rifle is. I learned my lesson quite a few years ago. I purchased a lovely pre-WWII drilling in 7x57R (so marked) and following the first shot, a straight wall case emerged. Someone had lengthened the chamber into some rimmed wildcat making it dangerously thin-walled.
I would hang it on the wall behind the bar.
I agree as to the facts above wholeheartedly. The conclusions are a bit pessimistic, as I think I'd have better than 50% chance of getting the gun serviceable. Nonetheless, the pessimism is probably a mission of mercy because I see $1000 of work in that gun to make it clean, tight, and presentable IF the bores and walls are good. Seeing the gun, rebrowned and cleaned up in serviceable condition is worth $900-$1200, it would be cheaper to pay someone to kick you in the balls, take a grand from your wallet, and call it a day.
For the sadist, the steps to get the gun going again (determine it is safe) go like this:
1.) Meticulous measurements of the wall thickness of the shotgun tubes, a tricky task since a drilling has a lot of ribs that can conceal dangerous thin spots.
2.) Clean and inspect chamber and bores of all three.
3.) Chamber cast and slug the 9.3x72r to verify it is suitable.
4.) Check that the gun is tight and "on face".
5.) Strip the barrels. Rebrown them. Retrace the engraving optional.
6.) Clean checkering, recut and touch up borders and rounded spots.
7.) Repair or replace the butt plate or pad. (they all need something in this area)
8.) Take the gun apart, carefully clean and lubricate. Time and adjust screws.
9.) Address unforeseen issues discovered along the way, unless 1-2-3-4 indicate the gun is a wall hanger.
