  We propose a scheme to measure the quantized Hall conductivity of an
ultracold Fermi gas initially prepared in a topological (Chern) insulating
phase, and driven by a constant force. We show that the time evolution of the
center of mass, after releasing the cloud, provides a direct and clear
signature of the topologically invariant Chern number. We discuss the validity
of this scheme, highlighting the importance of driving the system with a
sufficiently strong force to displace the cloud over measurable distances while
avoiding band-mixing effects. The unusual shapes of the driven atomic cloud are
qualitatively discussed in terms of a semi-classical approach.
