It's the first time I see Serena Williams' tattoo on the nape of her neck. Is it a heart (as fellow blogger Rich thinks, the former number one might be revealing secret love to the world) or possibly some symbol? You see how the lines on the top of the heart are crossed, that doesn't seem to be just a regular heart.
Additional info: At the Olympic Tennis Event fourth-seeded Serena was knocked out by Russian Elena Dementieva in the quarterfinals. Williams' game was sloppy in the previous round against Alize Cornet, and she didn't manage to raise her game enough to fight off Dementieva, despite powering through the opening set. Losing to the Russian 3-6 6-4 6-3 chances of an all-Williams final at the Olympics have been ruined.