  We use observations of the Luminous Blue Variable (LBV) P Cygni spanning
seven decades, along with signal processing methods, to identify a periodicity
in the stellar luminosity. We find a distinct period of $4.7 \pm 0.3$ years
together with shorter periods. The periodicity is a possible indication of a
binary companion passing in an eclipse-like event from the dense LBV wind, and
if so it is the first observational indication that P Cygni is a binary system.
This may support models that contribute giant LBV eruptions to interaction with
a binary companion. We discuss other interpretations for the periodicity as
well.
