"I am inclined to think someone walking past has seen the large amount of clothes and rubbish left on the front porch as donations and perhaps been interested in what's there.
"The felt pen may have even been left as part of one of the donations," she said.
Forrest said donated goods were not her department and she had asked the Red Cross North Island retail manager to see if donated goods could be cleared from the front of the building each day of the Christmas and New Year break.
"This hasn't happened and it may well have been a catalyst to the graffiti."
Although disappointed with the tagging, she said at least the building had not been broken into or windows smashed, which had happened "over and over" in the past.
"We've installed bars on windows and alarms in an attempt to stop the damage, this latest incident is a nuisance more than anything."
Forrest said she had planned to "look around" for some help to get rid of the tagging but hadn't had a chance to do it yet.
"If there was someone out there with a bit of spare time and a little know-how, it would be greatly appreciated."