What does it mean to have `seen' the quark-gluon plasma?

Identifying the quark-gluon plasma requires convincing experimental evidence that partons move independently throughout the environment created in a heavy ion collision and with densities expected from equilibrium considerations. In lattice calculations, charge correlations suggest that quarks exist independently, and are not merely exchanged from hadronic object to another. Many experimental signatures (J/Psi suppression, quark number scaling, etc.) suggest that quarks are not confined to their original singlets, but these signatures do not make a clear case that quarks move independently or that they have the expected densities. I discuss a class of measurements that parallel lattice observables and has the prospect of investigating whether partonic charges move independently.