Residents said they've spotted several mailboxes in Inwood and Washington Heights with a sticky substance inside. View Full Caption DNAinfo/Mat Katz

WASHINGTON HEIGHTS — Police have arrested three mail scammers for "fishing" envelopes out of Uptown postal boxes, officials said — after locals warned they've spotted several mailboxes with glue along the inside lid to trap letters as they’re placed inside.

Three individuals were arrested on Dec. 15 at 156th Street and Amsterdam Avenue at approximately 1:20 a.m. for pulling out letters inside, according to NYPD sources and Donna Harris, spokeswoman for the U.S. Postal Inspection Service.

Details of the arrests and the identities of the individuals were not immediately available.

But locals say they've been warning of rigged postal boxes throughout Washington Heights and Inwood for weeks.

Inwood resident Dave Thom was mailing Christmas cards on Saturday at the mailbox on West 218th Street and Park Terrace East when “I noticed that several [envelopes] got stuck to the inside of the lid and realized that it was coated in several places with a clear sticky substance."

"I unstuck my letters and then came back with a plain sheet of 8.5 x 11 paper to cover the sticky surface and prevent anyone else from falling victim," he added.

Another resident, who wished to remain anonymous, said his wife was also mailing out Christmas cards last week when she noticed two stuck envelopes inside the mailbox on the corner of 215th Street and Indian Road.

When he walked to the mailbox again on Sunday, he said he noticed a mail truck and told the driver about the incidents. He said the driver responded that he already knew of the issue. They both then looked inside the mailbox and noticed a spot of glue inside the lid.

Residents said mailboxes along 204th Street and Broadway as well as at 190th Street and Fort Washington Avenue, have also been compromised.

Thom said he also notified the U.S. postal inspection services Sunday, but the office told him they had not received any incident reports from Inwood.

There have been a rash of mail thefts reported recently in Harlem, where the Center for Urban Community Services discovered $56,000 in checks were stolen, forged and cashed after they were mailed from East 119th Street and Lexington Avenue.

READ MORE: Stolen Checks Taken From East Harlem Mailboxes Total $20K: NYPD

Rash of Check Thefts From East Harlem Mailboxes Claims 2 More Victims: NYPD

Earlier this year, police said scammers were targeting a series of mailboxes in the Upper West Side, by sticking a sticky substance to a piece of cardboard or the mailbox and “fishing” for whatever sticks to the area.

Inwood residents have taken some matters into their own hands, including covering and removing the sticky substance to prevent others from falling victims to the scam.

"It would be great if everyone in Inwood put a piece of plain paper over sticky lids," Thom said, adding that it's a pretty inexpensive fix guaranteed to annoying the thieves.

Harris added that mailbox fishing scams are “not just a holiday thing.”

“It can happen at any time,” Harris added.

Harris said residents that suspect a suspicious activity with a mailbox should report it to the police, her office and notify the postal office. Her office’s command center at 212-330-2400 is open 24 hours.

Residents can also use the mailbox at the post office if they have concerns about on-street mailboxes, Harris said.