General Motors Corp.'s Cadillac launched its 1997 Seville STS last week with a spot featuring "NYPD Blue" star Dennis Franz. Driving the sedan and affecting a coplike demeanor, Mr. Franz pulls over a Mercedes owner and "writes him up" for driving an underpowered luxury car. Two other spots in the estimated $50 million push, from D'Arcy Masius Benton & Bowles, Troy, Mich., also created the new tag: "The power is yours." The estimated $50 million push has two other spots are due later this month. One stars "Cybill's" Christine Baranski and the other "In Living Color's" Damon Wayans. Copywriter: Rob Hendrickson. Art director: Alan Rado.