  Using an advanced version of the hadron resonance gas model we have found
indications for irregularities in data for hadrons produced in relativistic
heavy-ion collisions. These include an abrupt change of the effective number of
degrees of freedom, a change of the slope of the ratio of lambda hyperons to
protons at laboratory energies 8.6--11.6 AGeV, as well as highly correlated
plateaus in the collision-energy dependence of the entropy per baryon, total
pion number per baryon, and thermal pion number per baryon at laboratory
energies 6.9-11.6 AGeV. Also, we observe a sharp peak in the dimensionless
trace anomaly at a laboratory energy of 11.6 AGeV. On the basis of the
generalized shock-adiabat model we demonstrate that these observations give
evidence for the anomalous thermodynamic properties of the mixed phase at its
boundary to the quark-gluon plasma. We argue that the trace-anomaly peak and
the local minimum of the generalized specific volume observed at a laboratory
energy of 11.6 AGeV provide a signal for the formation of a mixed phase between
the quark-gluon plasma and the hadron phase. This naturally explains the change
of slope in the energy dependence of the yield of lambda hyperons per proton at
a laboratory energy of 8.6 GeV.
