A recent spate of postal box thefts has put postal authorities on high alert and raised concern that customers may be vulnerable to identity theft.
But authorities said it was unclear whether the brazen heists were part of a trend.
"The economy the way it is, there is an increase in crime all around," said U.S. Postal Inspector Renee Focht of the Postal Service's Los Angeles division, which has jurisdiction over Southern California. "We can't speculate why the mailboxes are being targeted."
Focht said fewer than a dozen of the boxes had been stolen in Southern California since the beginning of June.
As well as being swiped from in front of post offices, the blue collection boxes, which weigh about 200 pounds, had been uprooted from residential neighborhoods and business parks, Focht said.
"It does take some effort," said Focht said. "They're bolted into the concrete."
Four of the boxes were taken in less than a week from several San Fernando Valley post offices, including in Pacoima, Glendale and Burbank.