[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
generalized to covers over stop/reset switches on disk drives and
networking equipment. In hardware catalogues, you'll see
the much less interesting description "guarded button".