MONROE, Wash.—An online advertisement offered $28.50 an hour to anyone who wore a blue, long-sleeved shirt, yellow safety vest, eye protection and ventilator mask and waited near a bank.

Apparently, it should have been labeled “decoys wanted.”

Police said a number of people wearing the specified outfit were waiting near a Bank of America branch Tuesday when a similarly dressed man accosted a Brinks armored truck guard with pepper spray during a cash delivery in Monroe, a town about 25 miles northeast of Seattle. Police said the man grabbed a bag of money and eluded pursuers after entering a nearby creek.

FBI agents were trying to determine the source of the ad posted on craiglist.org, which ostensibly was seeking landscaping help on a city project, Monroe police spokeswoman Debbie Willis said.

As of Thursday morning no one had been arrested and the source of the ad remained undetermined, FBI Agent Roberta A. Burroughs said.

She told The Herald of Everett that she had never heard of a similar tactic in 15 years of investigating bank holdups.

The amount of money taken was not disclosed. It was not immediately clear how many workers showed up because of the ad. “The e-mail specifically said to wear a blue shirt and said, ’If a project manager is not there, do not leave,”’ said Mike Stevenson, 30, of Bremerton, one of several prospective workers who gathered at a Monroe park.