  There has been a striking realization that physics resolving the black hole
information paradox could imply postmerger gravitational wave echoes. We here
report on evidence for echoes from the LIGO compact binary merger events,
GW151226, GW170104, GW170608, GW170814, as well as the neutron star merger
GW170817. There is a signal for each event with a $p$-value of order 1% or
sometimes significantly less. Our study begins with the comparison of echoes
from a variety of horizonless exotic compact objects. Next we investigate the
effects of spin. The identification of the more generic features of echoes then
leads to the development of relatively simple windowing methods, in both time
and frequency space, to extract a signal from noise. The time delay between
echoes is inversely related to the spacing between the spectral resonances, and
it is advantageous to look directly for this resonance structure. We find time
delays for the first four events that are consistent with a simple model that
accounts for mass and spin of the final object, while for the neutron star
merger the final mass and spin are constrained.
