Per the title, according to the Irish legend of the leprechauns, at the end of every rainbow found after a rainstorm is where they hide their precious pot of gold. See more
Mr. O'Hanlan, how did you do that?
Ah, we all have our little secrets, don't we, Miss Wonder Woman?
[Wonder Woman's smile tuns into a look of surprise, until O'Hanlan starts laughing. Then she flashes her enchanting smile just in time for the final freeze frame