The Mercury Street office of Headway, which supports adults with acquired brain injuries, was sprayed with graffiti on Monday night. Two vans, as well as signage, were covered in bright pink scrawl.

Manager of the service Robyn Russell said the premises had been targeted by vandals "half a dozen times" in the past year alone, and many more times before that.

"We've been struggling with graffiti on our sign for some time. We clean it off, which is hard to do, but we put up with it," Ms Russell said. "But when we arrived [on Tuesday], we saw that whoever did it had jumped the fence onto our property and sprayed two of our vehicles. They've never done that before."

She said Headway clients had been distressed by the vandalism, and that money meant to support clients would have to be diverted to cleaning costs.

"This upset the staff, but more so, it has a negative effect on our clients. It takes money and time away from helping them. We can't afford to keep doing this."

She said the service would look into beefing up security to deter any future vandals from turning their attention on the Headway premises.

Anyone with information on the graffiti should contact Crime Stoppers on 1800 333 000.