Upon arrival in Los Angeles, McLain was a machinist with Perry and Woodward Company for three years and then joined the Griffith and Lynch Lumber Company, but he was best known for his ownership of an advertising, or bill-posting business.
McLain's rival in the advertising field was E.W. Campbell, who complained to the City Council in May 1893 that McLain, who was then in partnership with Lehman, was allowed to post his advertising bills on a fire-engine house next to the Plaza but that Campbell was not.