I don't know that any casino ashtrays have been 'restored' yet, but I've seen myself the artwork that was used for a number of the older glass ashtrays. With the prices moving into the multi-thousand dollar area, it's just a matter of time before someone decides to take a blank (or cheap ashtray with the same blank) and re-screens the image of a scarce ashtry on the bottom. This is not a difficult process. It can be done even if you don't have the right artwork by color-copying a real ashtray and making screens that way.

Beware of expensive ashtrays offered at prices that look "too good to be true"!