Who actually knows Saitama is as strong as he is? Other than Genos, King, and those he's defeated(if they even knew they were fighting him), who else knows his secret? It seemed to me the Hero Assoc. still hasn't taken a real notice.
Going by the chapter 102 of the Shonen Jump Manga:


   Genos, King, Silver Fang, Blizzard, and (possibly) Mumen Rider