Check out this repop Wolf's Head Oil sign from Germany. Looks like all of these rusty back signs are coming out of Argentina and Germany. Same MO...hammer chips on the mounting holes, weathering, rusty black back and bidder ID kept private. And of course, "Date and place of origin unknown".

http://cgi.ebay.com/Wolfs-Head-Oil-Ename...1QQcmdZViewItem