It is indeed a slang term for Canadian tank crews. Affectionately of course.
No idea on the other uses...never heard it outside or inside the military only other than what it was used for our tank and LVT crew nicknames.
For example, I'm Army Signals as a trade - our nickname was SigsPig. Interesting enough, due to cross training we all had, some of us were zipperpigs. It meant you were trained on the LVT/tank and were a signals operator inside. What delinates a typical Canadian soldier, if I was part of the tank crew, I could drive, fire any weapon, and use the comms equipment. Every tank crew had a zipperpig as a role, but our diverse training meant we also could do other roles.
As for Sigspig - is a derivative of signals pinger - old WWII term for radio and radar/sonar operator on a ship and radar on land. It just devolved into SigsPigs in the 60's-70's-80's ¯\_(ツ)_/¯
