  Compelling evidence for the creation of a new form of matter has been claimed
to be found in Pb+Pb collisions at SPS. We discuss the uniqueness of often
proposed experimental signatures for quark matter formation in relativistic
heavy ion collisions. It is demonstrated that so far none of the proposed
signals like J\psi meson production/suppression, strangeness enhancement,
dileptons, and directed flow unambigiously show that a phase of deconfined
matter has been formed in SPS Pb+Pb collisions. We emphasize the need for
systematic future measurements to search for simultaneous irregularities in the
excitation functions of several observables in order to come close to pinning
the properties of hot, dense QCD matter from data.
