The NYPD is training thousands of officers how specifically to prevent thefts and other crimes of opportunity on the subway, and says it's already seen results since the initiative launched a few weeks ago.

Officers, both plainclothed and uniformed, are spotting professional thieves before they strike on the subway. Det. Eric Larson, who's been on the transit beat for more than a decade, is helping train the newer officers and says there are suspicious behavioral patterns that are common among many criminals.

A favorite technique of subway thieves, for example, is crowding.

"These criminals in a subway, when they commit their crime, they have to be close," he said. "So what they're going to do is be on top of you, be unnecessarily close to you. This is uncomfortable, they might even be touching you."

One surveillance video showed it in play: a thief, with his right hand covered by dry cleaning, grabs cash from open bags while passengers are stopped at the turnstile. (Watch video above.)

Police say a subway rider can tell if someone's too close: "Just take a look at their feet, and take a look at the space to the right or left of them. Do they have enough room to move back?"

"If someone's too close," Larson said, "excuse yourself from the situation and move to the empty space."

Thieves also like to target victims sitting close to the doors because it makes for a quick escape, police said.

Another favorite place is platform benches, like in a case seen on another in which a thief uses a razor blade to cut the pants pocket of a sleeping victim. (Watch video above.)

"His right hand is making a cutting motion. He removes a wallet," Larson pointed out. "The passenger is not moving. He's sound asleep."

Captain Jonathan Bobin, commanding officer of the Transit Bureau Response Team who's overseeing the training, says the NYPD is sharing its crime-smart strategy directly with passengers. During one canvassing trip Monday, he reminded waiting riders to zip their bags and put their phones away or hold onto it when a door opens on the subway so that no one can snatch it out of their hands.

Larson urges riders to be aware, for themselves and others at all times.

"Even though we're out there -- we are in uniform, we are in plainclothes -- we can't be everywhere. You as a rider have to take in consideration safety."