Here's where things get even more crazy. Some people are now combining an old theory – that Meera Reed, the girl currently with Bran, is actually Jon Snow's twin sister – with this other theory about Jon Snow's parentage; hence the R+L=J+M.
Despite the fact that Jon Snow looks a hell of a lot older than Meera in the TV series, this impressively in-depth Wiki of Ice and Fire lists the birth years of both characters as 283 AC – which would make them the same age. When you add in the fact that Lyanna Stark is also listed by the Wiki as dying in 283 AC (and Meera's supposed father Howland Reed was with Ned at the Tower of Joy on the day they went to find Lyanna), it seems like there's more than enough ground for a good old fan theory.