Source : Free On-Line Dictionary of Computing

molly-guard
     
        /mol'ee-gard/ [University of Illinois] A shield to prevent
        tripping of some {Big Red Switch} by clumsy or ignorant hands.
        Originally used of the plexiglass covers improvised for the
        BRS on an IBM 4341 after a programmer's toddler daughter
        (named Molly) frobbed it twice in one day.  Later generalised
        to covers over stop/reset switches on disk drives and
        networking equipment.
     
        [{Jargon File}]