I agree that it seems redundant to design new pictograms, but I don't think just going with an international standard is necessarily better. It's all about conveying the message as effectively as possible, and to this end I think the pictograms have to be evaluated on a case by case basis.
My personal starting point is the
USDOT list of pictograms, which were created to based on existing pictograms, and in many ways are similar to the ISO ones. Many of the DOT symbols are internationally recognized, and used widely in airports with lots of international travelers.
Here's a complete list of the symbols:
http://www.aiga.org/symbol-signs/
Looking through the list there are some issues though, most noticeably when it comes to ail signage. Toronto has (or will have) four to six distinctive types of rail transit, each with it's own properties. Here's my count:
Subway
Streetcar
LRT (coming)
GO
UPX
Amtrak/VIA and potentially other intercity rail (ONR?)
And since there will be signage there, none of the pictograms can be confused with the Pearson Link Train.
There is only one rail icon in the DOT set, and three in the ISO set; Rail, Subway and Tram. Assuming we will need at least four pictograms (Subway, Streetcar, LRT and Heavy Rail) we come up short with both lists. The ISO rail pictograms come closest, but none of them really reflect anything in use in the area today. Therefore, there is a need for other logos, and in this case I think it would be best to go with the most widely recognized local symbols, those being Streetcar and Subway to start. These symbols are already in wide use locally, and clear enough that visitors should be able to pick it up quickly. This leaves LRT, for which a new or existing pictogram must be picked, as well as heavy rail, which is another issue altogether, especially since GO changed their logo a few years back so it no longer represents all types of rail.
I don't think we can jut pick a set of existing pictograms and say "use these" without examining them in detail.