Letter braids stemmed from a kind of self-challenge a few years ago: "Hmm, I wonder if I could braid a symbol into someone's hair?" The @-sign was first, and a trend was born! It's since been suggested that I should try to get the whole alphabet.
So far, I've only done braid-writing using dutch braids, since they are easiest to work with, hold well, and the braid is easily visible.
For more pictures of letter braids I've done, see the Flickr set here.