In the comics, Rex Tyler, aka Hourman, was a scientist who invented a vitamin called 'miraclo', which gave him super speed and super strength for a single hour. "Miraclo" was re-dubbed "mirakuru" and used as a key plot device in the second season of Legends of Tomorrow parent series, "Arrow".
The Justice Society of America that Rex Tyler (Hourman) mentions at the end of the episode is the Earth 2 equivalent to the Justice League of America.
The Justice Society of America, mentioned by Rex Tyler/Hourman, was the first superhero team ever written. At its creation, it included characters from two different comic book companies, including the Flash (Jay Garrick), Hourman, Sandman, Dr. Fate, and the original versions of Hawkman and Atom. When DC comics rebooted some of its heroes starting in 1956, it created the more well-known Justice League of America, featuring the versions of the Flash, Atom and other heroes that appear in the current comics and television series.
Rex Tyler, aka Hourman, says he's a member of the Justice Society of America. In a previous episode of "The Flash", the Gideon computer owned by Eobard Thawne says that Barry Allen is a "founding member of....". The Golden Age Flash, Jay Garrick, was a founding member of the Justice Society.