Four banks have been held up in the Washington area since Saturday, in robberies that occurred in varied locations and employed differing techniques, but had at least one thing in common: In each case, the robber wore a hat.

Hats may be appropriate winter attire, but it also appeared likely that the headgear was intended to reduce the value of surveillance photos, which were obtained in all four robberies.

Two occurred in Fairfax County, Saturday and Monday. In each, photos show the robber wearing a white construction helmet.

Police said that the two robberies may be linked.

Monday’s robbery occurred about 2:45 p.m. at the BB&T branch in the 6000 block of Fort Hunt Road in the Mount Vernon area. The robber demanded cash and fled with an undisclosed amount.

Saturday’s occurred around noon at the Wells Fargo Bank branch in the 6100 block of Franconia Road in the Franconia area. Cash was demanded and received. No gun was shown in either robbery.

A robbery occurred Saturday in the Potomac area of Montgomery County when a man entered the M&T branch on River Road and showed a note, police said. They said a gun was implied but not seen. The robber fled with cash. He wore a black hat, police said.

The fourth robbery occurred about 4:45 p.m. Monday at a PNC bank branch in the Ellicott City area of Howard County.

The robber walked into the bank, in the 4300 block of Montgomery Road, with a hat that covered his face, police said. A bank employee confronted him, and the robber showed a gun.

It was not clear whether the hat prompted the confrontation.

The robber then demanded money from a teller, received some and fled.

In the photo, which shows the man at the teller’s window, he appeared to be wearing a patterned, knitted hat, possibly with earflaps.

The hat is pulled low on his forehead. He is holding a pistol in his left hand, and it appears to have an extended magazine.

No arrests had been reported as of late Wednesday.