Sam Asghari Tells Fans He and Newly-Engaged Britney Spears Will Sign a Prenup

Britney Spears' newly-minted fiance, Sam Asghari, says he and Britney will sign a prenup, alright ... a prenup designed to protect HIM. Sam was responding to fans who urged Britney to get a prenup ... his response -- yep, they'll sign an "iron clad…