Police are offering a cash reward to catch a graffiti vandal.
The Central neighbourhood police team (NPT) will give £50 to anyone who can help them catch the spray can vandals.
Images of a yellow bird and name tags have appeared on walls in the Kirkgate subway and on New Brunswick Street in the city centre.
Insp Richard Close, of the Central NPT, said: “Graffiti is vandalism, it lowers the tone of an area and makes people feel unsafe.
“In order to improve the area the local authority then spends hundreds of pounds cleaning the walls only for it to be replaced.
“Good art work can be appreciated, famous artist such as Banksy can be admired. None of the graffiti I have seen is of the same high standard or appropriately placed with the consent of the property owners.
“If we establish who is responsible for the vandalism they will be prosecuted and if appropriate instructed to clean the paintings off assisting the local authority.”
Anyone with any information should call the NPT on 101.