This is the stamp of the Eesti Kunstiakadeemia or the Estonian Academy of Art. All the student work is stamped with this stamp. This was not my experience at art school in Australia.

Hallmarking can only be done by a licensed hallmarker! So unless you sit the rigorous test to become a hallmarker, in Estonia you are not allowed to stamp your work with a 925 or carat stamp! You get in trouble if you do. You can go to prison. You can send your work to get tested by the hallmarker and then stamped, but if you’re like me and you fly by the seat of your pants at the last minute, I’d never be organised enough to get this done. This practice seems a bit archaic to me but maybe it’s common.