  Arnold (2005), Forgan (2013), and Korpela et al. (2015) noted that
planet-sized artificial structures could be discovered with Kepler as they
transit their host star. We present a general discussion of transiting
megastructures, and enumerate ten potential ways their anomalous silhouettes,
orbits, and transmission properties would distinguish them from exoplanets. We
also enumerate the natural sources of such signatures.
  Several anomalous objects, such as KIC 12557548 and CoRoT-29, have
variability in depth consistent with Arnold's prediction and/or an asymmetric
shape consistent with Forgan's model. Since well motivated physical models have
so far provided natural explanations for these signals, the ETI hypothesis is
not warranted for these objects, but they still serve as useful examples of how
nonstandard transit signatures might be identified and interpreted in a SETI
context. Boyajian et al. 2015 recently announced KIC 8462852, an object with a
bizarre light curve consistent with a "swarm" of megastructures. We suggest
this is an outstanding SETI target.
  We develop the normalized information content statistic $M$ to quantify the
information content in a signal embedded in a discrete series of bounded
measurements, such as variable transit depths, and show that it can be used to
distinguish among constant sources, interstellar beacons, and naturally
stochastic or artificial, information-rich signals. We apply this formalism to
KIC 12557548 and a specific form of beacon suggested by Arnold to illustrate
its utility.
