You know the rainbow flag you see around to show gay pride? It didn't always exist.
It was actually invented by an American artist; an ex-soldier in fact (maybe that explains his love of flags) named Gilbert Baker. He came up with it in 1978, and since then, well, it's taken off in a big way as the most obvious international symbol for queers.
When you're travelling in a foreign country and see one outside a bar, club or B&B, even if you don't speak the language, you know you're with friends.
It gets waved in gay pride parades from India to Israel and New York to Auckland. The rainbow has been turned into jewellery, t-shirts, just about anything you care to imagine. A lot of straights actually don't realise what it's for, so in some countries it can be a useful discreet signal.
The different stripes all had separate meanings originally, but now they're mainly seen as symbolising the variety you find in the queer world, and how we all fit together to make something beautiful.
Visibility is good - it's easy for gays to feel like we don't have any strong identity in the bigger straight world, and the flag is a great way to show a bit of visibility, to let the world know we exist and aren't going anywhere.
You gotta say it was a stroke of genius from Baker - after all who can hate a rainbow?