The 1973 Lemmings stage show at the Village Gate in New York City was promoted with a poster that was never seen in the magazine or used for the soundtrack LP. (Slight correction: A version of it did appear in the National Lampoon Songbook. Thanks, Jeff!) It featured a beautiful illustration by James Grashow. I remember seeing it in graphic design annuals back in the seventies. There is a copy of it on view at this auction site. (For a larger image, click here.) (Thanks to Rollo for the link.)