I don't think Symbols are technically unique between exchanges, since some exchanges are very old, although I would have trouble coming up with an example where

I don't think Symbols are technically unique between exchanges, since some exchanges are very old, although I would have trouble coming up with an example where the major US exchanges have conflicts. Given that the Google Finance has a search bar prominently on the page. I would expect/hope that the top result would be used in the event of a conflict. It's very probably in the event of a conflict that one of the potential companies is very common while the rest are niche listings on foreign exchanges anyway.