As Rick W. rightly pointed out, most of the presentation Luger pistols with monograms on the chambers were on the 1900 Lugers and most were cased without the 'GL' hallmark. I believe that the serial range of these presentation/gift pistols fell in the 5000 range. I do have a few serial numbers of these Lugers in my notes which are unaccessible at the moment.
If I was to take a guess where a 1906 'GL' Presentation Luger (with monogram) would fall, I would say in the 55000 serial range.
Albert
Imperial Arms