ESPN has signed Keyshawn Johnson as an NFL studio analyst, assigning him to the network’s two key football franchises: “Monday Night Countdown” (7-8:30 p.m. ET) and “Sunday NFL Countdown” (11 a.m.-1 p.m. ET).Johnson announced his retirement on Wednesday as a player after an 11-year career in the NFL. He was an All Pro wide receiver, leading the Tampa Bay Buccaneers to a Super Bowl championship. As part of his deal, Johnson will write weekly columns for ESPN.com and appear on ESPN Radio’s new NFL show hosted by Chris Mortensen and Bill Parcells. Johnson auditioned for the job when he served as a guest analyst during ESPN’s exhaustive coverage of the 2007 NFL Draft last month. “He delivered passionate opinions and candid analysis,” said ESPN exec veep Norby Williamson.