Know Your Space Invaders
Before Halo, before Gears of War, before Doom, there was Space Invaders: the first intergalactic shoot 'em up video game. If you're a child of the 80s you probably spent way too many hours at the arcade or with your Atari playing this classic game.
A French artist, known only as "Invader," has taken the alien figures from the game and transposed them to the streets of the whole world. Using ceramic tiles he constructs small (and sometimes mural sized) invaders on various city structures. According to Wikipedia he has spread his art "throughout the world since the 1990s, among more than 30 cities over 5 continents".
Los Angeles has its share of space invaders strewn across the city. Most of the smaller pieces have been removed, either by store owners or by collectors/eBay douchebags. Check out his site to see some of his previous "invasion" in Los Angeles.
Bonus Round: A video of Invader at work.