If it follows standard Russian military marking practice, there should be a date code next to the serial number; for a while in the 50s and 60s, Makarovs had a two-letter date code that filled in as a date code, but the PSM entered production too late for that style of marking. This only goes for military-issued PSMs, though, and Izhevsk has started making civilian versions of the pistol (in both 5.45 and 6.35 Browning) as the IZh-75 that don't have any obvious date markings, but should have a date stamp next to the proofs, though you may need to strip the pistol down to see them.
