The suspect walked into the shop around 3:30 p.m. last Tuesday, May 28, authorities said in a release.
He asked to see some watches that were on display and snatched one off the tray after an employee removed them from a locked case, according to police. Investigators said the watch was worth $40,000.
The suspect fled the store and ran through a back hallway, authorities said.
He's described as a tall black man with a muscular build and a black goatee. Police said he was wearing a multi-colored, rugby-style, long-sleeve Ralph Lauren shirt, ripped jeans, and sunglasses.
Anyone with information is asked to call UMPD at 610-265-3232 or submit a tip through Crimewatch.
Click here to follow Daily Voice Feasterville-Trevose and receive free news updates.