They said the suspect stopped a motorist Tuesday morning near the area of 147th Street and Inglewood Avenue in the city of Lawndale.
When the driver asked the man what sheriff's station he was assigned to, the suspect got onto his motorcycle and sped off.
Investigators described the suspect as a white man, 35 to 40 years old. He was wearing a tan uniform shirt and green pants. The badge he was wearing appeared to be a fake.
Officials said to protect yourself from illegitimate traffic stops, try to pull over in a well-lit area, ask the officer or deputy to identify himself or herself and be aware of any strange requests or overly personal questions.