There are at least 4 artist with the moniker XO:
1. XO was created by Canadian singer-songwriter The Weeknd, as an unofficial imprint to release 3 mixtapes in 2011.
2. XO are an American shoegaze/alternative rock band from Atlanta, Georgia. The band consists of twin brothers Jeff (guitar, vocals) and Jacob (bass, vocals) Turner, who also perform in the band Say Anything. Live, the band are joined by guitarist Joe Assef and drummer Parker Case, who also plays drums on some studio tracks. Read more on Last.fm