MONTPELIER, Vt. (AP) — A prison inmate who makes stationery and license plates pulled a fast one on state police by adding the image of a pig to the state decal on their cruisers.

On the 16-inch car door decals, made by prisoners in Windsor, one of the spots on a cow in a scene with mountains and a pine tree has been changed to the shape of a pig, a derogatory term for police.

A Vermont state trooper discovered the pig while inspecting his vehicle on Wednesday. State police say they believe the decals have been added to about 30 cruisers in the past year.

About 60 altered decals were made over the last couple of years, said Andy Pallito, commissioner of the Department of Corrections, which is looking into who made the modification and when.

New decals will be made by Monday at a cost of $780. The expense will be covered by a surplus in the revolving fund that supports the offender work program, Pallito said.

State police Maj. Bill Sheets wasn’t amused by the prank.

“While some may find humor in the decal modifications, the joke unfortunately comes at the expense of the taxpayers,” he said Thursday.

The Burlington Free Press newspaper first reported the pig decals.