Forget the bag checks. Theatergoers entering New World Stages to see the latest jukebox musical should be forced to present their birth certificates. Featuring more than two dozen pop hits from the 1960s in its period-set tale of an aspiring photographer arriving in New York City to achieve her dreams, A Sign of the Times doles out beloved songs to its baby boomer target audiences with the regularity of a food pellet machine. It’s force-fed nostalgia, to be sure, but plenty of fun, at least if you were born between 1946 and 1964 and owned a radio.