The robber approached the window and asked for a pen to write on what the teller thought was a check, according to police. He put the robbery note in the teller's drawer and she gave him the money, police said.
The man fled north on Cramer's Alley and was last seen at the rear of the 100 block of North Potomac Street.
Police describe the robber as a white man in his 20s, weighing 160 pounds and about 5 feet, 6 inches tall.
At the time of the robbery, he wore a white sleeveless T-shirt and gray sweat pants. His dark hair was pulled back in a ponytail held by a purple band.
Shortly after the robbery, the bank locked its doors as a police officer interviewed the teller inside. Customers approaching the window in vehicles were turned away as another teller explained there had been a robbery.
The Federal Bureau of Investigation was assisting in the investigation. The bank is insured by the Federal Deposit Insurance Corp. and the FBI routinely helps with bank robberies, Hoover said.
It was the second bank robbery in Hagerstown this year, according to Lt. John Moulton. There have been four bank robberies in Washington County in 1999.
The other three bank robberies this year were at Hagerstown Trust Co. branches. The first was on Dual Highway March 4, the second was March 15 on West Side Avenue and the third was in Maugansville July 21.
Anyone with information may contact Detectives George Brandt or Hoover at the Hagerstown Police Department at 301-790-3700, ext. 234 or the local FBI office at 301-663-3469.