Scrabble Tile ring which I found on Folksy.com from the BeautifulShinyDiamonds shop.
It's really retro and an absolute bargain at only £3 plus p+p. Elly at BeautifulShinyDiamonds will even present it in a lovely gift box for an extra couple of quid. This would make a fabby birthday present for someone who likes kitsch jewellery.
The ring is adjustable too, which means it should suit everyone! And other letters are available, so you're not limited. Have a look at some of Elly's other items too - some really cool stuff!