Thieves use bottles coated in a sticky substance to "fish" items out of mailboxes, police said. View Full Caption NYPD

UPPER EAST SIDE — A series of U.S. Postal Service mailboxes in the neighborhood have recently been targets of "fishing" scams, in which thieves use a sticky substance to pull out money and checks belonging to unsuspecting victims, the NYPD said.

The 19th Precinct reported that the following mailboxes were recently targeted, according to an email sent to the community Tuesday:

► East 64th Street and Park Avenue

► East 69th Street and Fifth Avenue

► East 75th Street and Second Avenue

► East 86th Street and Park Avenue

► East 91st Street and Madison Avenue

► East 93rd Street and Second Avenue

► East 95th Street and Fifth Avenue

An additional mailbox was targeted in June on East 90th Street and Park Avenue, where four men were arrested for stealing checks totaling more than $3,000, prosecutors said.

Police did not provide information about the other seven thefts, including dates and what was stolen.

When thieves want to grab items from mailboxes, they attach a string to a sticky object — like a glue mouse trap or a bottle with glue smeared on it — and drop it into a box so they can fish the items out, according to the 19th Precinct.

The perpetrators then pocket the cash or change the checks using nail polish remover before writing in a bigger sum and cashing them, police said.

The 19th Precinct shared photos of recently discovered tools from another precinct, both of which were bottles coated in a sticky substances and dangled from a shoelace.

In some cases, thieves have also stolen a USPS employee's key ring to open the mailboxes, police said.

East Harlem residents have been dealing with similar thefts, as more than $140,000 had been stolen from a dozen or more victims between August 2016 to early May.

► READ: Postal Detectives Flummoxed by Mail Thieves as 2 More Victims Come Forward

Police recommended that residents drop all mail off directly at the post office rather than using the blue mailboxes if there's money or gift cards involved.

"If you notice anyone lingering around any mailbox generally in the evening hours and overnight, or notice any fishing paraphernalia (sticky traps, string, bottles) in or around the mailbox please call 911 to alert us," the 19th Precinct wrote in its email.

Donna Harris, a spokeswoman for the U.S. Postal Inspection Service, advised people to call the USPS's 24-hour command center at (212) 330-2400 if they see a suspicious substance on a mailbox, but to first call 911 if they see someone tampering with a mailbox.

"We know of some instances in areas of Manhattan, especially on the Upper East Side with mailbox fishing," she said. "We're investigating and using technology to prevent this and working with the NYPD. We're in the process of modifying collection boxes. We're also attending community council meetings to let the community know how to prevent their mail from being stolen."