Is this what you meant?
see section 2.6 of this document
I see the other sites want money for the documentation. I'm not sure if this is what you're after. Hope it helps.
EDIT: ok .... try this link ISO Concept Database
You can select one of the tabs accross the top and view some of the standards for symbology, etc. If you look at my printscreen, I went under the "graphical symbols" tab, then I selected "transport facilities" and hit the search button. If you fish around in here, you might at least get a sense of what you're dealing with and be able to get a feel for the standards. Is this closer to what you were after? I think I'm out of ideas! I hope this at least puts you on the right track to answering your question.