  We present a simple method for the identification of weak signals associated
with gravitational wave events. Its application reveals a signal with the same
time lag as the GW150914 event in the released LIGO strain data with a
significance around $3.2\sigma$. This signal starts about 10 minutes before
GW150914 and lasts for about 45 minutes. Subsequent tests suggest that this
signal is likely to be due to external sources.
