The closest to it is Czechoslovakian ‚‚goose‚‚ mark for 14 K gold that has remained unchanged since 1921. If so, it is Art Deco diamond set in black onyx.
Take a look here (ZLATO, image far right in yellow).https://ceskamincovna.cz/en/czech-hallm ... ucts-1004/
Maker cannot be identified. Contacted Czech Assay Office Prague some time ago. No archives with makers.
Austrian ‚‚bird‚‚mark for silver gold combination is different, straight,long beak, just recalling, have no reference with me.