I'm reviving this post, because I think I may have solved the hole in the trigger guard mystery.
Download Attachment: lock.jpg
Someone brought this to my attention on ebay about a month ago. Curious as to what it could be for. I instantly remembered Lugerlou's post about the hole in the trigger guard of the 1910. I beleive this a pistol lock used to secure a pistol to an armory rack. It has a reciprocating double hasp. It slides from one end to the other.
Download Attachment: lock2.jpg
The shank of the hasp is approximately 1/4" in diameter. Just about the same size as the hole in the Luger trigger guard.
Download Attachment: lock3.jpg
The body of the lock has what appears to be a styleized Luger stamped in it. With the Large block 74, a V in a circle, and "HEN TA" below. The style of the marks appears to be Finnish or Scandinavian, but I suppose, could be German. The lock would be applied by slipping the hasp through the hole in the trigger guard. Easy access would mandate that the Luger be stored upside down. Which is a commom method of storing handguns in an armory. And then hooked around a securing device of some kind, maybe a rod secured to a rack.
Anybody want to dive in with different ideas or comments. Feel free! Ron