The Cheshire cat, in English popular culture, is an ever-smiling cat, capable of appearing and disappearing at will. It can even gradually fade away, leaving only its smile visible. "Laughing like a Cheshire cat" is an expression used since the 17th century to refer to someone who laughs with their teeth and gums showing.
     The cat was also brought to life by the writer Lewis Carroll in some of Alice's adventures.
The T-shirt image comes from the flyer Leidenthal designed for three Big Brother & The Holding Company (Janis Joplin's band) concerts at the Matrix in San Francisco, from April 25th to 27th. from 1967.