Herbert William Mullin was an American serial killer born on April 18, 1947 who operated in Santa Cruz, CA. 
Mullin was serving life in prison for 13 murders which he says he committed to prevent further natural disasters.  Mullin died of natural causes on August 18, 2022.

4" x 6 1/2" back portion of an envelope with Mullin's handwriting on which he asking a friend if they have heard of a band named the Outlaws.
He has drawn a smiley face using the two question marks.