Personally, I think it is a "play on words" or the normal PMD sign.
There for a while some people were coming up with Garage signs with interesting modifications to the normal Pontiac Motor Division.
I belonged for several years to the Royal Pontiac Club of America.
Dr. Eric M. Schiffer was the president of the club and tied in heavily with
Jim Wangers. Eric owns Wangers' "Black Bird"
https://www.thevrl.com/profile/DrEricMSchiffer
I have little knowledge of the signs produced. He might know more.
Do not think it was a actual PMD sign though.
Tom V.