The billboards thank Stephen Harper for "Ten Years of Excellence".
It’s not clear who paid for the ad, but PC Party leader Ric McIver says the message is well deserved.
"It never hurts to say thank you to anybody that does a good job for you and works hard and puts their life on hold for a decade and clearly Prime Minister Harper did that and there's many Canadians, I'm one of them that is grateful for that and this is, I guess, an unofficial sincere gesture saying thank you," he said.
McIver tweeted a picture of a similar sign on display at MP Jason Kenney’s Christmas open house two weeks ago.
The former Prime Minister has been keeping a low profile since the October election, though an Edmonton Oilers fan took pictures of himself with Harper in Las Vegas last month.