ON THE TOWN: Prince celebrated his 28th...

ON THE TOWN: Prince celebrated his 28th birthday last weekend in Detroit, where the Purple One played a two-hour show (much of the time bare-chested). The concert featured a “Happy Birthday” sing-along as well as some intriguing remarks near the end of the concert about his recent L.A. date. “This is a lot better than Los Angeles,” he said with a mysterious grin, adding later, “There are birthdays and then there are birthdays !” On hand to enjoy the festivities were such backstage visitors as Bob Seger, Magic Johnson, George Clinton and Emmanuelle Sallet, the French model who co-stars in his upcoming film “Under the Cherry Moon.” A film crew was on the hand to shoot the show, though there is no official word on where the footage will turn up. . . . Meanwhile, in Chicago last weekend, the city hosted its Third Annual Blues Festival, which featured a surprise appearance by Keith Richards, who jammed with Chuck Berry and, clutching a bottle of Jack Daniels, swapped stories backstage with blues legend Willie Dixon. Also on hand were Bo Diddley, John Lee Hooker, Frank Frost, Albert King, Robert Cray and Pops Staples and the Staples Singers. . . . Ex-Sex Pistol Steve Jones wasn’t the only old rock warrior to show up at some of Charlie Sexton’s Roxy shows last weekend (hey-- everyone seems old next to the 17-year-old guitar wiz). Last weekend, Stiv Bators also came up on stage to help out with a raucous version of Bowie’s “Rebel Rebel,” though Stiv’s locks looked positively puny compared to Sexton’s sky-high do. . . . And get those scooters out of the garage. The Cavern Club, a favorite pit-stop for local psychedelic warriors, has launched a a series of Friday night Mod shows, spotlighting area Mod bands as well as visiting groups like the Jet Set and the Risk.