Chula Vista neighbors are on the lookout for a thief who may be targeting a specific item in mailboxes.
"It's unnerving when you wonder who is going through neighborhood stealing mail," said Chuck Gavrilovich.
Along Paseo La Cresta and nearby streets, a rash of thefts have made many residents anxious.
Even a postal worker has started warning neighbors that someone is going around stealing mail.
On Monday, Carmen Coverdale said one of her neighbors who had put some bills in the mail got a call from Chase Bank.
"Chase said someone had written a check out for cash," said Coverdale.
It was a check written for $500, but the neighbor wasn't missing any checks.
"It's called whitewash," said Coverdale.
It appears the check was originally one put in the mail to pay a bill, but it was altered in a process known as "washing."
According to law enforcement experts, a chemical solution dissolves away the ink in certain parts of the check, which allows a thief to fill out a blank check. Typically, thieves will keep it under a certain amount to avoid triggering security protocol at banks.
More than a decade ago, a thief washed one of Coverdale's checks. When she saw the fraudulent one, she noticed it was discolored.
Gavrilovich has also felt the sting of check washing.
"Our checks were blue and came back greenish," said Gavrilovich.
No arrests have been made in the most recent check fraud case.
Experts say it's a good idea to mail checks in locking mailboxes or at the post office. High-security pens and checks can also help thwart check washers.