The incident happened on March 4 at the Wine and Spirits Store located on the 3700 block of L Street.
Police say the male suspect walked into the store around 6 p.m. and approached the counter to buy a bottle of wine.
He told the clerk he had to go get his wallet and briefly left the store.
When he came back, he handed the cashier a note demanding money and lifted his shirt to show a gun in his waistband.
The robber got away with an unknown amount of cash from the register before fleeing north through the parking lot then east on Erie Avenue.
Police describe the suspect as a white or Hispanic male, 30 years-old and 5'7" tall with a medium build. He was wearing a white hooded sweatshirt with a red shirt underneath, blue jeans, black gloves, and a rust colored knit hat.
If you recognize this man, call police at 215.686.TIPS (8477) or text a tip to PPD TIP (773847).
All tips will remain confidential.