A security camera captured the suspect inside ER Diamonds on South 11th Street.
He walked inside on Thursday, May 28, and asked to see a watch that was displayed in a front window case.
The woman allowed him to try the watch on. But as soon as it was around his wrist he ran from the store without paying.
The suspect was wearing a white shirt with black sleeves and a red decal on the front.
Anyone with information should contact Central Detective Division: (215) 686-3093.