F L Selgstlader simply means Friedrich Langenhan Auto loader. With the mono-gram grips, and the roll mark of D.R.G.M over 625263, it should be the Open Model, with a small window cut into the frame. I believe it was made prior to 1921. It was modified from the original model because the slide kept blowing back into the shooters face. Value depends on condition, and only a picture can determine that. It is listed at 400 in excellent condition down to 100 in poor. That's just a retail guide or what you would pay if you brought it at a gun store.
Knowing the background of this gun, you couldn't pay me to shoot it.