  We show how the difference between the finite temperature T structure
factors, called S_-, associated with spin and density, can be used as a
indication of superfluidity in ultracold Fermi gases. This observation can be
exploited in two photon Bragg scattering experiments on gases which undergo
BCS- Bose Einstein condensation crossover. Essential to our calculations is a
proper incorporation of spin and particle number conservation laws which lead
to compatibility at general T with two f-sum rules. Because it is applicable to
general scattering lengths, a measurement of S- can be a useful, direct
approach for establishing where superfluidity occurs.
