"Use a cane; go to prison" joke

(From the "San Jose Mercury News," May 17, 1989:)
David St. John, 37, was the victim last week of what police
say was a terrible mistake.
The two Hayward police officers used their batons to hit
St. John, who they didn't realize was blind, after mistaking
his collapsible cane for an illegal martial arts weapon, said
Lt. Mitchell Penn, the police department's internal affairs officer.
"It was a very regrettable incident," Penn said Tuesday. "But from
what I've seen so far it's not a case of overzealous officers.
They had no idea he was blind-they were extremely upset when they
found out."
Field training officer Eric Ristram said St. John placed in his pants
pocket what appeared to be a nunchaku, a martial arts weapon consisting of
two round sticks of wood connect by a chain.
The officers thought the man could see their uniforms so they didn't
identify themselves when they told St. John to hand over the contents
of his pockets.
St. John said later he thought he was about to be mugged.