Do you have balloon races?
Here, before release, a local address can be attached to the balloon, then when they land people who find them can write back to say where they got to. Schools use it to interest children in geography and local heritage.
A friend had one land from the UK in his garden in the UK, so he took it with him on his next business trip to Cologne and sent a postcard and photos back of the withered balloon by local landmarks.
A famous one was this:http://news.bbc.co.uk/1/hi/england/beds/bucks/herts/8310816.stm
The balloons do have addresses attached - it's not a race as in a competition, but finders of the balloons are invited to write back to say "hello" and where the balloon got to. Most of the time when I released a balloon as a child, though, nothing came back. I guess most are just going down somewhere where they will never be found.
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