They scrawled “ITFC” on a vast artwork on the side of King Street’s Dragon Hall depicting plants, animals and a dragon.
The initials were daubed on the street art on Saturday by visiting Town fans, who watched their side defeat Norwich City 2-0 at nearby Carrow Road.
Locals said another nearby hoarding had “f*** off Norwich City” written on it, but this has since been removed.
Joey La Mèche, 37, an artist who has a studio on the street and helped paint the mural said: “As if the win was not enough. It is a shame.
“Unfortunately like any street level art it is subject to graffiti.
Joey La Mèche, (Image: Submitted)
“In this case it was probably an Ipswich supporter who thought he was being clever.”
Claire Bagnall, 58, who grew up in the street said: “It’s a bit of salt in the wound. It digs a little deeper.
“Even if you’re not a football fan you can’t help getting caught up in the rivalry.”
The mural at Dragon Hall (Image: Jack Warren)