(in a circle)
T is a service designation of the New York City Subway. It is not currently in use, but was previously used for a service on the BMT West End Line, originally BMT 3.
T is also the proposed future designation of service on the planned Second Avenue Subway line. T trains would make stops along Second Avenue from 125th Street in Harlem to Hanover Square in the Financial District.
T currently appears on rollsigns as a black letter on a white circle; see Unused New York City Subway service labels for more information.