This probably has occurred to someone else at some time, and maybe it had even appeared in the comic books, in some form. But I was thinking about how we really don't know who the Joker's "civilian" identity is/was, and then, the oddball portion of my mind wondered if we, maybe, had been kind of saying his name all along: Joe Kerr (or a variant spelling of his surname). Kind of like the Penguin's going by the name P.N. Gwynn, on the '60s Batman series.