This John Plocher design, the HO DCC Flag man, gives the Time Table and Train Order (TT&TO) operator a convenient way to "flag out" and warn other trains that he's occupying main track, it also serves as handy DCC track power tester!  The Flag man has contacts that bridge the track (and trigger occupancy circuits) and light a 2 LED "lanterns" to warn approaching trains of his presence.  The 4-pack part is a revised design by John Plocher with all Surface Mount LEDs, greatly simplifying assembly.  You will need to solder the Flag man's body to his base. Weights are supplied. 

Assembly Instructions

Also available in an 8 pack