The pin is a U.S. Navy Command at Sea insignia. When worn above the ribbons on the left breast, it signifies the wearer is presently in command of a sea-going unit (ship or squadron). When worn below the ribbons, it signifies that the wearer has previously served in a command at sea billet. The markings on the back might be some personalized markings, or they could be manufacturer's marks.
I don’t know much about it - it’s not on California’s approved list, so I’ll never see one here. It does get a pretty good review here: http://www.gunblast.com/Kel-Tec_Sub2000.htm