The credit to Seattle Slew for the manure is a joke. (The numerous comments in the Trivia section has apparently led some people to believe it's on the level.)
As Harper Valley P.T.A. (1978) concludes, Will proposes to Stella and she accepted his proposal. As they get in the helicopter and start for their trip, a note on a long & clear plastic banner, of "STELLA JOHNSON FOR MAYOR" (in red capital letters) is tied on the tail of the helicopter, trailing behind them.