A well-worn piece of advice that circulates among the streetwise is composed of three simple words: Watch your back.

And three incidents that occurred in the District last week demonstrated that the old advice is still good.

Although robberies are down sharply this year compared with 2013, at least three people lost property on city streets in two days to robbers who came up behind them.

Two of the robberies occurred during daylight hours in the fast-developing, rapidly gentrifying H Street NE corridor.

It was about 12:15 p.m. Thursday, police said, and the female victim was walking in the 900 block of H Street NE.

An unknown person, according to a posting on a police e-mail discussion group, “approached the victim from behind and snatched a chain from her neck.”

The robber fled west on H Street.

On Wednesday, police said, a male victim was walking to a bus stop in the 700 block of 10th Street NE “when he was approached from behind” by a robber who punched him in the back of the head. The victim fell, and a second robber grabbed his cellphone.

Police said one robber fled south on 10th and the other caught a bus on nearby H Street.

The third robbery also occurred on Wednesday, late at night in the Bloomingdale area, another fast-gentrifying section of the city.

The victim was at a bus stop in the 1800 block of North Capitol Street, a couple of blocks south of Rhode Island Avenue NW. It was about 10:40 p.m. and, police reported, “someone walked up behind” him and hit him in the head with a pipe.

The robber fled with the victim’s wallet and cellphone, police said.

The extent of any injury could not be determined.

Through Thursday, the number of robberies in the city in which no gun was shown was about 23 percent less than last year at this time.

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