The zigzag ramp from the sidewalk leads to a door here, with two signs:

DO NOT ENTER, MBTA EMERGENCY EXIT ONLY

DANGER, LIVE TRAINS - NO ENTRY WITHOUT FLAGGER, FOR ACCESS CALL GREEN LINE DISPATCH AT 617-nnn-nnnn, DO NOT ENTER

The footpath beyond here exists, but is only accessible to the public if the Union Square station is being evacuated in an emergency situation, so it should be marked as locked or inaccessible or similar. 