Hi Dean,
I could be off on the date, but I think with some 1968 gun legislation...guns began being marked when imported.
Some of the military, Swiss lugers in the USA without the import marks may have been brought in before that 1968 date...I have several Swiss military issue lugers (having the +/V or the +/M inspector stamps) that do not have import markings...so I assume they came into the States prior to that time period.
Regards,
Pete... <img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" />