I really like the detail of the new sign brackets/mounts. The square relief around the perimeter and in the corner really plays into the architectural details of the station. For this reason I would shy away from options B, C & D as I believe they undermine this small but important design detail. While improving the wayfinding; the diagonal, the rounded, and the white border do not necessarily play into the design details of the station as a whole.
Can I suggest a mock up based on option A whereby all vertical elements "or lines" are removed except where they divide directions. Additionally if the proper logos were used to replace text this would allow uniform widths and spacings. Ie. Replace "Air Canada Center" text with logo of same dimensions as TTC logo.
Something like this perhaps?
View attachment 53996
All aesthetics aside, in terms of straight-up "wayfinding function", I think option C is the best bet but could definitely use some interface tweaking. The way Union/Metrolinx have chosen to display the platform numbers is just outright silly.