  Context: The $\gamma$-ray blazar PKS 2155-304 has attracted considerable
attention because of its extreme TeV variability characteristics during an
exceptional flaring period in 2006. Among the observed key findings are (i) a
minimum variability timescale as short as $\sim 200$ sec and (ii) highly
variable TeV emission, which in the frequency interval [$10^{-4}$ Hz, $10^{-2}$
Hz] can be described by a log-normal distribution and suggests an underlying
multiplicative (and not additive) process. Aims: Simultaneously accounting for
these findings appears difficult within conventional approaches. Following
earlier suggestions for the TeV blazar Mkn 501, we explore a possible scenario
where PKS 2155-304 is supposed to harbor a supermassive binary black hole
system and where the observed TeV variability is dominated by emission from the
less massive black hole. Methods: We analyze the constraints on the very high
energy (VHE) source imposed by the observed variability characteristics and the
integrated VHE luminosity output, and discuss its implications for a binary
black hole system. Results: We show that for a secondary mass of $m_{\rm BH}
\sim 10^7 M_{\odot}$, fluctuations in the disk accretion rate that feed the jet
could account for the observed red-noise type variability process down to
frequencies of $\sim 10^{-2}$ Hz. Jet curvature induced by orbital motion, on
the other hand, could further relax constraints on the intrinsic jet speeds.
Conclusions: Because a binary system can lead to different (yet not
independent) periodicities in different energy bands, a longterm (quasi-)
periodicity analysis could offer important insights into the real nature of the
central engine of PKS~2155-304.
