Unfortunately, the only reference I could find for an "urn mark" referred to an old Portugese firm. [The site's World Silver Standards chart indicates .800 fineness extends to Portugal only as "current" era.] Here is a more extensive discussion of world standards to show when and where 800 fineness was known to be acceptable: viewtopic.php?f=26&t=5137&p=10176&hilit=portugal+800#p10176
Without a Crescent/Crown mark to accompany the 800 mark, Germany (post-1886 era) does not seem possible.
Perhaps a full shot of the object may aid the identification process? Because any individual marks can relate to maker firms, assayers, retailers or even workers this could take some time for someone to bring more insight.