answer is coming late, but better than never. Reason is that I just joined this site and now started reading back through the postings.
Your Dreyse 07 marked "L.P.D.Memel No.175" is a pre-WW1 german police pistol. The mark reads "Landes Polizei Direktion Memel, Weapon No. 175", Landespolizeidirektion (today written in one word, but in that time abbreviated and written either seperated or with -, like Landes-Polizei-Direktion) means, roughly translated, "county police department", "Memel" naming the geographical area around the river Memel, which in that time was part of the German Reich, today belonging to Poland, Estonia, Lithuania or Lathvia, I am not so good in geography to give the exact borders, sorry.
There are several other police markings like yours known, I own another Dreyse with "P.D.P. No.xxx" from the "Polizei Direktion Potsdam" and have seen a picture of another one with "Sächs.Gend.No.xxx" for "Sächsische Gendarmerie", meaning Saxonian Gendarmerie.
So far there has no official order been found which gives exact instructions about marking pre-WW1 police weapons. Only two orders are known from Prussia, the first from 1922 and the second from 1932, but nothing from before 1922.
It would be great to see some pictures of your gun, if you dont want to post them on the net contact me in a personal mail.