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.
 
Two separate writings from Mullin - Quinalt and Humongous Buteo. 

The first is approximately 3" x 4 1/4" and is unsigned.
The second is also 3" x 4 1/4" and is hand signed on the back, H.W. Mullin.