I have marked my magazines with either a black or silver Sharpie. The caliber and a number (of mags). The markings rub may rub off, but I just touch 'em up. Works for me.
Good to see someone else here has a P345. When I went to buy a .45, a 1911 was too large/heavy for me. I used to carry one in the service. In my old age, the P345 was near perfect. smaller, narrower, lighter. Even my wife enjoyed shooting a mag worth of ammo through it. First and only time though as she passed shortly thereafter, but she got downright giddy after shooting that P345. A great memory for me.