With the Sheppard Subway, the old font made a comeback, at least for the station names at platform level, and here, and and the large station names above entrances, should be used exclusively. However, directional signs should really be in an easy-to-read font, though I love the B-D stations and their exclusive use of the old font on the old metal signs (my favourite being Keele's complex metal signage at platform level).
But only use Helvetica and the TTC font, don't mix things up more than that, and be consistant in the use of each. I hate the station names in the Yonge station redos from Union to College, and Rosedale through Davisville, and the Spadina Line.