There are no station announcements to signal to riders which train will arrive first. There are no countdown clocks. And so the travelers help one another, communicating the hints they have trained their senses to capture: the pitch of a screech when a train comes to a halt — unique depending on the line, some insist; the rustling of newspapers, windswept by an oncoming train; the wave of a hand, the nod of a head, a pull on the top of a baseball cap, like a third-base coach advising his player to steal.