Skateboard, aka Monty Holmes, was a 48 year-old legless pandhandler who lived on the streets in San Francisco's Tenderloin district.
This memorial sprang up on Taylor Street after Skateboard was run over and killed while crossing the street by a mail truck on April 24th. This event didn't seem to surprise anyone, as he was known as a reckless drunk who often darted into traffic without warning. He was also well liked in the neighborhood and is survived by his wife Linda Thomas. I've encountered Skateboard many times, often on the way to baseball games at Pac Bell Park.
You can read more about the life and death of Skateboard at SF Gate:

http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/04/26/BAG5MPFCK631.DTL