luger magazine marks

[lboos]

Bar44. ive only been into the luger world fof 3 or 4 mo,s. and i own one luger, but on my mag. it also has the + and the 63. i was looking at a book named Luger, and there was a pic. of a mag. with these same marking,s, the book said the + stood for the extra mag. that came with the gun?
im sure one of experts here well get us both stright on the +. LB.