the M used to go Downtown with the J then continue into South Brooklyn. So train doors would open at Bowery and Canal St in opposite directions and both trains would announce simultaneously, “This is a Brooklyn-bound M train”
someone got on the m train next to me and asked another rider if this was the queens-bound direction. they responded that both ways on the m-train go to queens and you could see the confused question asker’s brain blue-screen in real time