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.