Discarded mail has been found in the areas of Terrace Drive, Hillman Avenue and Arbor Avenue in the past week, Capt. Patrick Halleran said.
Police learned of the thefts from the Belmont post office, which has received complaints about stolen mail from residents in the past week, he said.
Investigators believe the thief or thieves walk through the neighborhood, steal the mail from boxes, take what they want and then discard the rest, Halleran said.
Police warn that residents who have their mail stolen can become victims of identity theft, he said.
Residents are advised to report any suspicious people or activity to police, and are encouraged to have their mail delivered through a slot inside their home or a locked mailbox, he said.
Anyone with information on the thefts is asked to call Belmont police at (650) 595-7400 or the department’s crime tip line at (650) 598-3000.