Right, so True American is the definition — over in the States they call an honest, straight-talking person a straight shooter. For the wordplay, build it piece by piece: STRAIGHT gives you "pure", then S is the abbreviation for "son", then HOOTER is your "siren". The word "chasing" tells you the order — the siren has to come after the pure son, so you stack them up as STRAIGHT plus S plus HOOTER to land on the answer.