The RX sign

"There's no stopping Tom Waits", is Bob Dylan's reaction to the regular e-mail contributions by Tom Waits on his Theme Time Radio Hour. 

Here's a clip (mp3) from the episode of Feb. 19, 2008 about "Doctors", in which Waits explains the origins of the RX sign.

And Dylan also played Day after tomorrow during the "War" episode (Nov. 19, 2008).