John Lennon Autograph from Beatles Last American Appearance

My mother-in-law got John Lennon's autograph from a friend who worked at Candlestick Park in San Francisco.
He apparently worked for security or something that gave him access to where they walked in.

The autograph was written on the move and is sloppy. It was written on a time sheet that was ripped so it does not have any date or clarification that it is from Candlestick Park. It has been sitting in a frame in a closet with the marker that was used to sign the autograph since 1966. how can I authenticate this and get a value?