The coroner's office released sketches of the victim on Tuesday and is asking for the public's help in learning his identity.
The man, estimated to be between 60 and 75 years old, was struck by a southbound train at the East Fifth Avenue track crossing at about 4:45 p.m. on June 21, Coroner Robert Foucrault said.
He was not carrying any identification, and an extensive search, including of DMV and military records, has yielded no results.
The victim was riding a "Go-Go Pride Mobility" scooter when he was struck, Foucrault said. The serial numbers on the scooter had been scratched off.
The man was described as white, about 5 feet 5 inches tall and weighing about 130 pounds. He had brown eyes, a gray moustache and gray and silver hair that was cut in a flat-top.
He was last seen wearing a black Fumagalli pea coat, an Old Navy button-down black short-sleeve shirt, black Old Navy pants, black socks and black leather shoes.
Anyone who might have information about the victim or the case is asked to call the San Mateo County coroner's office at (650) 312-5562.