It might look familiar because it was a preliminary concept for the first letter that AS sends you in The Room. Maybe it reminded you of that note or one of the others that appears in the games?

It sound plausible, but I think there are 2 things that don’t make sense to me. First, the initials on the stamp (the red thing) aren’t AS, but I think it says R&F or RS, it’s hard to make out. Second, I have a memory of my first time playing The Room 1 on kindle fire and for some reason, I remember a scene before you are taken to the title screen. It had something like a statue or something like that on the ground of a person with a child (I think?) and next to it was a note similar to that, then I entered the building and came to the title screen. It’s possible this could have been a really vivid dream, but I’m not sure, and it’s weird because how would I dream about a letter that I had only known existed about 6 years later? This is way too long for it’s own good, but that’s my response.

The initials on the seal I think I can explain - since this was a preliminary concept for the game, it's likely the developers went through a number of options for initials before settling on AS.

The statue thing I can not explain... I've played through the games many times myself and I don't remember ever seeing anything like that. I'd say it was probably a dream? Or maybe something from another game.