Yep, this is PMD, a maverick counterstamp that I've not before encountered, and I've seen tens of thousands of them, given that they're one of my major collecting interests.
This "3*" c/s appears tinier than most. It may have served as a jeweler's or other fine craftsman's mark. One key to identifying marks like this is to locate a known or highly attributable c/s that bears a matching mark. It's a rare occurrence, but it has been done!
Barring the extremely slim chance of this c/s being attributed, this maverick c/s renders the coin damaged, having minimal value as such. On the flip-side, attributed c/s's can greatly enhance the value of their host coins.