Hi Pete,
Congratulations for you new gun! I always love those early self-loading pistols and this was one of my finds. After some year looking for one - they aren�´t common here in Brazil - I get one which still has its oriinal finish, although pretty weary.
After some research I discovered that my Roth-Steyr is an early gun (serial number 66xx) and also found the unit where it served during WWI: the 15th Dragoon Regiment. After that I could also figured out it battle story - which was VERY, VERY interesting. As your gun also has the unit�´s stamp I would do the same if I was you. Just a tip.
Some more info about the roth-Steyr: these guns were developed specially to Mounted Troops (90,000 produced between 1907 and 1914) and some also saw service with some flying units - when it was unoficially called "Flieger Pistole".!
Here the picture of mine M-7:
Hope you enjoy.
Regards,
Douglas.