Source : Free On-Line Dictionary of Computing

pastie
     
        /pay'stee/ An adhesive label designed to be attached to a key
        on a keyboard to indicate some non-standard character which
        can be accessed through that key.  Pasties are likely to be
        used in APL environments, where almost every key is associated
        with a special character.  A pastie on the R key, for example,
        might remind the user that it is used to generate the rho
        character.  The term properly refers to nipple-concealing
        devices formerly worn by strippers in concession to
        indecent-exposure laws; compare {tits on a keyboard}.
     
        [{Jargon File}]