It has some sort of insignia and a serial number number on it aswell. Pictures in the link. Thanks!
Edit: He purchased**
I think it's a bayonet for a Mauser rifle produced by Oesterreichische Waffenfabrik-Gesellschaft from Steyr.
The hilt is typical for Mauser bayonets and the stamped WG indicates the Waffenfabrik-Gesellschaft. There should be OE for Oesterreichische right above (maybe you misidentified it as a crest?). Is there a stamp on the other side of the blade?
Mauser rifles and their bayonets were pretty widespread, without additional markings it will be hard to tell when and for whom it was produced. Could be anywhere from late 19th to mid-20th century.
Oh no I just realized I forgot to take a picture of the serial number. When I see him on tuesday ill take a picture of it.