A charge brought under Wanganui's gang patch ban bylaw has been dropped after the man argued the bulldog on his beanie was a Georgia University logo and not a Mongrel Mob insignia.

Police decided to withdraw the charge against Brett Beamsley, 45, who was pulled over by police while driving near his Aramoho home on September 2, a day after the bylaw came into force.

Before he could plead not guilty, the charge was dropped during an appearance in Wanganui District Court yesterday, the Dominion Post reported.

If the case is not reopened, police will have to return the confiscated beanie to Mr Beamsley, who said he would continue to wear it.

"As soon as I get it back again I'm straight to town to see if they arrest me again."

Central area commander Superintendent Russell Gibson said he was disappointed by the decision, which was made by at least one police staff member but without adequate consultation.

"I am concerned that the decision will be used to bait us, which is the very behaviour that the legislation was brought in to curb."

If the situation arose again it was highly likely police would proceed with a prosecution so it could be tested in a court of law."

Wanganui Mayor Michael Laws said the logo was obviously gang insignia.

He had accepted police assurances it was a simple error and wouldn't happen again.

Georgia University football team's mascot is Uga, a white bulldog which wears the team's colours of red and black - similar to Mongrel Mob colours.