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The polarization of quarkonium states produced in hadron collisions exhibitsstrong non-perturbative effects - for example, at small transverse momentum$p_t$ charmonia appear unpolarized, in sharp contradiction to the predictionsof perturbation theory. The quark--gluon plasma is expected to screen away thenon-perturbative physics; therefore those quarkonia which escape from theplasma should possess polarization as predicted by perturbative QCD. Weestimate the expected $J/\psi$ polarization at small $p_t$, and find that ittranslates into the asymmetry of the $e^+e^- (\mu^+\mu^-)$ angular distribution$W(\theta) \sim 1 + \alpha cos^2\theta$, with $\alpha \simeq 0.35 \div 0.4$.Comment: 4 pages, no figure

Quarkonium polarization in heavy ion collisions as a possible signature of the quark-gluon plasma