h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Well, here're a few sets of tips for Canadian signs.

Background colour of sign:
Green -- directions having to do with the roads. ie, telling what road you're on, distances to locations, and visual guides to what kind of choices are upcoming.
Blue (Que), Brown (Ont) -- tourist sign
White -- legislation. ie, speed limits, how they're enforced, littering, so on. On the 401 there are even big signs explaining the penalties for various speeds over the limit. Of course, when travelling 140k or higher, you don't really have the time to notice

Exit location. This is important. In Canada (and the U.S. in some places) you can have exits off the right-hand side of the road or the left-hand side of the road. This is actually indicated on the big signs over the road telling you how many kilometers are left to the exit. On top of the sign to either the left or the right will be a small tab with the exit number on it. In Quebec, these things are even highlighted in yellow. If the tab is on the left, the exit will be on the left. If the tab is on the right (the norm), the exit will be on the right.