Why rockstars demand that all the brown M&Ms be removed

The legendary "no brown M&Ms" contract clause was indeed real, but the purported motivation for it was not. The M&Ms provision was included in Van Halen's contracts not as an act of caprice, but because it served a practical purpose: to provide an easy way of determining whether the technical specifications of the contract had been thoroughly read (and complied with).

Read more at http://www.snopes.com/music/artists/vanhalen.asp

It's a useful tool for all kinds of contracts. If you want to spot-check compliance, sprinkle in a few random bits.