  We study the time evolution of a rotating condensate, that expands after
being suddenly released from the confining trap, by solving the hydrodynamic
equations of irrotational superfluids. For slow initial rotation speeds,
$\Omega_{0}$, we find that the condensate's angular velocity increases rapidly
to a maximum value and this is accompanied by a minimum in the deformation of
the condensate in the rotating plane. During the expansion the sample makes a
global rotation of approximately $\pi/2$, where the exact value depends on
$\Omega_{0}$. This minimum deformation can serve as an easily detectable
signature of superfluidity in a Bose--Einstein condensate.
