Cmdr. Ian Lafreniere noted that incidents often occur in the days preceding and following the oft-violent annual March 15 protest.
"We're talking about vehicles that were burned (and) damages to vehicles and property of the Montreal police," he said in an interview.
He added that several symbols were found along with the pig's head.
"It looked like people who were looking for publicity —and it did work, in fact," Lafreniere said.
The macabre discovery was made by an employee who was arriving for work Friday morning.
The head was placed on top of a pentagram that was scrawled on the ground.
Several wooden branches in the shape of what appeared to a human form were also attached to the main doors.
Lafreniere said the note mentioned people who were missing.
Police investigators hope video surveillance will help them find the person behind the incident.
Lafreniere also reminded organizers of Sunday's protest to share their itinerary so the demonstration would be legal.