Few people would like to be regarded as so heartless as to refuse to give a stranger the time of day. But many people no longer wear wristwatches, and the combination of these circumstances have apparently made some people crime victims.

Multiple incidents have occurred throughout the District, according to a D.C. police official, in which robbers have taken smartphones after approaching victims on the street and inquiring about the time.

When, in an effort to be polite, people have pulled their phones from their pockets, robbers have grabbed them and run, according to police.

The tactic is on the increase, police Cmdr. Daniel Hickson of the First District said in a posting on a community e-mail discussion group.

He suggested that the method has been devised by robbers in response to efforts by smartphone owners to protect themselves against the very kind of loss to which they fell victim.

Many people have recounted incidents in which they have been robbed of their phones while using them openly on the street. A robber snatches the phone from the user’s hands and flees.

As a result, the hazards of using or displaying smartphones on the streets, or in Metro trains and buses, have become the subject of numerous warnings.

Apparently, Hickson indicated, those warnings have been taken to heart. But, he said, robbers “are adjusting” to this preventive measure.

So in a kind of cat-and-mouse game between smartphone owners and smartphone thieves, it has apparently become necessary for the owners to refine their protective measures.

“I would like to suggest that individuals do not display their smart phones when responding to an inquiry for the time of day,” Hickson wrote. A watch could be consulted, he suggested, assuming the phone owner wears one.

The extent of watch-wearing in the age of smartphones seems to be unclear. By at least one report, posted online, watch-wearing depends on age, with younger people less likely to be equipped with a timepiece.

Hickson said that people could also respond to requests for the time by offering an estimate or professing ignorance.