  The observer-dependent tidal effects associated with the electric and
magnetic parts of the Riemann tensor with respect to an arbitrary family of
observers are discussed in a general spacetime in terms of certain "tidal
indicators." The features of such indicators are then explored by specializing
our considerations to the family of stationary circularly rotating observers in
the equatorial plane of the Kerr spacetime. There exist a number of observer
families which are special for several reasons and for each of them such
indicators are evaluated. The transformation laws of tidal indicators when
passing from one observer to another are also discussed, clarifying the
interplay among them. Our analysis shows that no equatorial plane circularly
rotating observer in the Kerr spacetime can ever measure a vanishing tidal
electric indicator, whereas the family of Carter's observers measures zero
tidal magnetic indicator.
