Someone has set fire to six American flags and five garden banners hanging outside homes in a five-week period, authorities said.
Police believe the vandal may be driving a gray or white pickup, but have few leads.
"Residents should be vigilant," Detective Jared Burns said Thursday. "If they see or hear anything suspicious, give the police a call."
All the vandalism has occurred in a neighborhood near the Whittwood Town Center in the the southeast area of the Los Angeles suburb.
Jupiter Street resident Tami Wysocki said an American flag outside her home was ignited about three weeks ago.
A new flag flies in its place.
"My husband was really upset," Wysocki said. "He's very patriotic."