A motorist on Route 22 reported Thursday that he saw a woman rolling paint on the same billboard that carries the graffiti ''Kill Bush,'' a crime that has sparked questions from the U.S. Secret Service.

The woman was spotted between 1:30 and 3 p.m. Monday in front of the billboard, south of the busy highway between Routes 191 and 512.

Colonial Regional police say the motorist did not see what the woman was painting on the previously stark-white billboard, which had been without an advertiser for some time.

The motorist, whom police declined to identify because of the ongoing investigation, gave little more description other than that the woman was a brunette, but police say the evidence is mounting.

Police say they will dust for fingerprints the packaging of a paint roller police recovered near the site in Hanover Township, Northampton County.

''It's a start,'' Colonial Regional Detective Gary Hammer said. ''We're very hopeful a suspect will be found.''

The tip came to police the day after the Secret Service began asking questions about the billboard vandalism. It is a federal crime to threaten the life of the president.

Hammer said the Secret Service had made no more contact with the Police Department since the initial inquiry.

The Secret Service could not be reached for comment.

Police have photographed the billboard, and the words may be taken off the billboard, Hammer said.

The billboard belongs to Harold S. Campbell Sr., owner of the Westgate Mall. Attorney Charles Bruno, who represents Westgate Mall and its managers, said Campbell's representatives had just learned of the graffiti Thursday and are taking steps to paint over it as soon as possible.

Police say they are certain that motorists had seen someone painting the sign. The billboard is in a field south of a busy highway. The headlights from vehicles make the area constantly visible, meaning the vandal or vandals could not hide at night.

The red letters, shadowed with grayish black paint, appear to be rolled on, which would take more time than spray-painting the words.

Hammer said police are investigating the incident as criminal mischief, which could range from a summary offense to a felony, depending on the extent of the damage. He did not have a cost estimate of the damage.

If authorities find the offender made a ''knowing'' and ''willful'' threat against the president, the vandal could face a federal charge that carries a sentence of fines and up to five years in prison.

Police are asking anyone who has information on the ''Kill Bush'' graffiti to call 610-837-4557.

nicole.mertz@mcall.com