The man then ran away with an undetermined amount of cash, police said.
City and state police searched the area but could not find the man, described as white, about 55 years old, with a heavy build and short brown and gray hair, wearing a tan jacket and light brown pants, police said.
Police suspect the same man could have pulled an armed robbery earlier that evening at the Tailor Cleaners in Walkersville being investigated by Maryland State Police.
That robbery occurred about 5:10 p.m. and netted about $35, troopers said.
A man entered the store, in the Discovery Shopping Center at 8429-A Woodsboro Pike, and announced a robbery, trooper said.
The man was described as white, about 6 feet tall and bulky, with mostly gray hair and a brownish-gray moustache, wearing a gray windbreaker and dark pants, trooper said.
The man threatened a female store employee with a handgun and demanded cash from the register, troopers said.
After receiving the cash, he ordered the employee to stay still in the rear of the store for 10 minutes and fled toward the rear of the shopping center, troopers said.
Police K-9 unsuccessfully searched the area, troopers said.
Anyone with information on the robberies is asked to call state police at 301-663-3101.