A sign held by a Maple Leafs fan outside the Air Canada Centre on Monday has triggered an avalanche of online outrage. 

Before Monday night's Game 3 between the Maple Leafs and Boston Bruins, photos surfaced online of a Leafs fan holding a sign that read "Toronto Stronger."

The message is a direct reference to "Boston Strong," a campaign that became a mantra in that city after the Boston Marathon bombings. The April 15 explosions killed three people and injured more than 260.

Shortly after the sign appeared, it triggered an angry response on Twitter, with many saying the sign was in bad taste in light of the Boston attacks.

"Overwhelmingly, the reaction has been that it was done in bad taste, that it was inappropriate, that it was classless," CBC sports reporter Carly Agro said on CBC News Network Tuesday.

Agro said there are unconfirmed reports that some fans inside the Air Canada Centre were chanting "Toronto stronger" during Monday’s game. 

"Certainly this is not being received well at all," said Agro, referring to the online reaction.

Agro pointed out that many Torontonians took part in a moment of silence that paid tribute to victims of the Boston bombings ahead of Sunday's Toronto Marathon.

Boston defeated Toronto 5-2 on Monday to take a 2-1 lead in the best-of-seven playoff series.

Claude Julien, the coach of the Boston Bruins, shrugged off the sign.

"Last night's sign, to me, had nothing to do with hockey," Julien said after practice Tuesday. "Boston Strong is about something that struck our city, not our team. Maybe it's a little sensitive for the Boston people.

"Those kind of things happen in playoffs. Unfortunately the best and sometimes the worst comes out of the passion of our game."

With files from The Canadian Press