  An expected signature of the presence of neutron stars in the population of
ultraluminous X-ray sources (ULXs) are large scale changes in X-ray luminosity,
as systems reach spin equilibrium and a propeller state ensues. We explore the
predicted luminosity changes when the disc is locally super-critical, finding
that a significant parameter space in dipole field strength and accretion rate
(at large radius) can be accompanied by changes of less than an order of
magnitude in luminosity. We discuss the spectral signature and locate three
ULXs (IC 342 X-1, Cir ULX-5 and NGC 1313 X-1) which appear to show changes
consistent with super-Eddington systems entering a propeller state, and place
rough constraints on the dipole field strength of NGC 1313 X-1 of $<$ 10$^{10}$
G. This work implies that the most reliable means by which to search for
putative propeller states will be to search for changes in hardness ratio and
at high energies.
