"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.