Two teenage girls were fined £80 for drawing chalk pictures on a pavement in Bangor, Gwynedd.
Hazel Mercer (pictured) and her friend Charli Lyth were fined £80
Hazel Mercer and her friend Charli Lyth, both 16, were given fixed penalties when a police officer saw them drawing hearts and rainbows.
One of the girls' fathers has vowed to fight the fine in court, adding the drawings were washed away by rain.
A North Wales Police spokeswoman said there had been a previous problem with graffiti nearby.
The girls said they were using "pavement chalks" to draw the pictures on a quiet residential street.
Their families claimed the pair were told they would be threatened with ASBOs if their graffiti continued.
Keith Marsh, Hazel's father, said he had been told to pay the fine within 28 days.
He said North Wales Police had since telephoned him and offered to reduce the fine to £40, but he told them to "forget it".
He added: "We'll go to court if necessary and I intend to make an official complaint.
"The police said there'd been a graffiti problem near the university, but that's a long way away and nothing to do with these girls.
"The girls paid £1 for 25 pavement chalks and they created girlie pictures on a path. What's wrong with that?"
A North Wales Police spokeswoman said: "Chalk graffiti has been a persistent problem in upper Bangor for quite some time, particularly around the university buildings.
"Whilst on patrol an officer found two teenage girls drawing pictures and symbols on the road. Both were dealt with by means of a fixed penalty."
She added there had been a problem near Bangor's university where a heavy-duty type of chalk had been used, requiring the use of special equipment to remove it.