It happened at the Presence Bank on South Third Street in Oxford back on September 11.
Investigators say officers arrived on the scene just minutes after the 9:05 a.m. robbery, but the man had already gotten away.
It's not yet known how much cash was taken.
Police want you to take a close look at his face, his hat and his jacket.
Anyone with information is asked to leave a tip on the police department's Crime Watch page or call the Oxford Police at 610-268-3171 and reference incident OP-25-04847.
Police are also asking that owners of residences and businesses near the area check their surveillance footage to see if it may have captured the suspect.