  We show how quantum oscillation measurements of surface states in an
insulator may allow to diagnose a strong topological insulator and distinguish
it from its weak or topologically trivial counterpart. The criterion is defined
by the parity of the number of fundamental frequencies in the surface-state
quantum oscillation spectrum: an even number of frequencies implies a weak or a
topologically trivial insulator, whereas an odd number points to a strong
topological insulator. We also discuss various aspects and issues related to
applying this criterion in practice.
