... as being an actual casino ashtray, it just might be a unique piece or possibly a gift shop item.

Though the three casinos did exist, I do not know of them being related in any way (which doesn't mean they weren't...).

If this helps any: I can show you plaques from Nice showing the same style hand painting as seen on your piece that are very rare and known to have actually come from the casino... but we do not know what purpose they served.

JB