I have been asked to determine the meaning of a stamp on the buttstock of a rifle which reads: Z Gefgs or Z-Gefgs (I'm working from a rubbing and am not sure of the prsence/absence of the -.) I'm assuming that Gfgs is probably Gefängnis = prison, but the Z has me stumped. Anybody familiar with this abbreviation?

Sorry I can't help with the translation - perhaps a good photo would help. I am curious to know what type of rifle this buttstock marking is on?