Source : Webster's Revised Unabridged Dictionary (1913)

Safety chain \Safety chain\
   (a) (Railroads) A normally slack chain for preventing
       excessive movement between a truck and a car body in
       sluing.
   (b) An auxiliary watch chain, secured to the clothes, usually
       out of sight, to prevent stealing of the watch.
   (c) A chain of sheet metal links with an elongated hole
       through each broad end, made up by doubling the first
       link on itself, slipping the next link through and
       doubling, and so on.