This is the identical labeling mechanism as tsiDigInpLabel1 but for this system's second general-purpose digital input contact, letting a site wire and label two independent external sensors or signals to this controller. It matters for the same reason: giving human-readable context to whatever site-specific condition, a second door, a smoke detector, an external alarm panel dry contact, has been wired to this particular input. An admin who's already used input 1 for a door sensor might wire input 2 to a water-detection sensor and label it accordingly here, so the two inputs' alarm histories remain distinguishable.