LordByron, I'm agreeing with the others here in that this is most certainly of European manufacture, but it might have been done during a period when marking or stamping the guns was not of the same import as it is now. This might predate WW I when there were many fewer gun makers and guessing who made something like this would have been fairly easy. After WW I and especially WW II, European and American economies boomed and anyone with $500 and an idea could start their own company, which is why testing and certification of high-pressure dangerous devices like firearms became more prevalent and they were marked by their manufacturers, testers, certifying agencies and the like.
Many of the older firearms companies that do not currently exist were absorbed by newer companies looking to grow. So unless it's Beretta or some other ancient manufacturer, it might become a real problem with no markings.
“Malo periculosam, libertatem quam quietam servitutem." (I prefer the tumult of liberty to the quiet of servitude.). Thomas Jefferson
"All that is necessary for the triumph of evil is that good men do nothing."
-Edmund Burke, Loosely translated from Thoughts on the Cause of Present Discontents. (1770)