KANSAS CITY, Mo. (AP) — A suburban Kansas City man's idea to place a "wanted" poster on billboards nine years ago has turned the giant highway signs into an important law enforcement tool.It's also aiding the search for Lisa Irwin, a Kansas City baby missing since Oct. 4.Roger Kemp of Leawood, Kan., was searching for the killer of his 19-year-old daughter Ali when it occurred to him that putting the suspect's picture on a billboard might inspire tips.The next year Kemp got his wish and a former area pool cleaner was arrested in Connecticut after two tipsters saw his likeness on a sign.Now law enforcement officials nationwide are turning to digital billboards to track down criminals and search for missing children.Opponents say the signs distract drivers and promote blight.