Robert Landau was 16, living near the Sunset Strip, when he looked up one day and saw John, Paul, George, and Ringo crossing the street on a billboard advertising Abbey Road. So he snapped a picture. It was 1969, and that sort of outsize signage for rock acts was a novelty. Hand painted, the images would stand for a month or so before making way for the next act. “They were extremely ephemeral, and very few people got to see them,” says Landau, who continued shooting the signs until record labels began pulling back in the early 1980s. The era’s gone, but you can see his photographs at the Skirball Cultural Center in a show inspired by Landau’s book, Rock ’n’ Roll Billboards of the Sunset Strip, which opens March 24.