NEW YORK — The NFL is stepping up its monitoring of on-field player activities to ensure that no one is flashing the hand signals of street gangs.

The Los Angeles Times reported Tuesday that the league had hired experts to look at game tapes and identify players or team officials who might be using suspected gang signals. Violators would be warned and disciplined if the episodes recurred.

League officials said Tuesday that avoiding gang-related activities has long been stressed.

They said the scrutiny was intensified after the shooting death of Denver cornerback Darrent Williams in 2007 after Williams was involved in a dispute with known gang members. Anti-gang information is included in orientation literature and stressed in the annual mandatory league meeting for rookies.

The NFL took further notice after Paul Pierce of the NBA's Boston Celtics was fined $25,000 in April for what the league said was a "menacing gesture" toward the Atlanta Hawks' bench. "I 100 percent do not in any way promote gang violence or anything close to it." Pierce said in a statement. "I am sorry if it was misinterpreted that way at Saturday's game."

The Times said that was the precipitating incident for the NFL.

"We were always suspicious that might be happening," it quoted Mike Pereira, the NFL's vice president of officiating, as saying of gang-related signals. "But the Paul Pierce thing is what brought it to light. When he was fined . . . that's when we said we need to take a look at it and see if we need to be aware of it."

Most senior NFL officials were at a league outing Tuesday and could not immediately be reached for comment.