Cal. Veh. Code § 25280

Vehicles operated by a local public entity, or pursuant to a permit, license, contract, or franchise with a local public entity, and used to collect and transport garbage, rubbish, or refuse may display flashing amber warning lights to the front, sides, or rear while stopped upon a street and actually engaged in the collection of garbage, rubbish, or refuse, or while moving between stops at a speed not greater than 10 miles per hour.