"mundus tuus est" or "orbis tuus est". Mundus mainly means world while orbis also describes circles (maybe you remember the pope blessing "urbi (city of Rome) et orbi"), I think it is somewhat poetical. Mh just pick the one that better fits the design of the tatoo 😉
If by "yours" you mean more than one person, replace "tuus" with "vester".
Edit: It's dead sure, mustpost's java applet and my dusty Latin book both said so 🙂
Oh, and if you are going to write Latin in capitals (Times font like), the old Romans wrote the capital U as V.