Calling the emission a "signal" immediately suggests it the artifact of some intelligence rather than an natural phenomena - and that has definately not been established yet.
Following is Googled definition of signal and I can't see any version of meaning which could imply something coming from a natural source:
1. a gesture, action, or sound that is used to convey information or instructions, typically by prearrangement between the parties concerned.
"the firing of the gun was the signal for a chain of beacons to be lit"
synonyms: gesture, sign, wave, gesticulation, cue, indication, warning, motion
"a signal to stop"
2. an electrical impulse or radio wave transmitted or received.
"equipment for receiving TV signals"
1. transmit information or instructions by means of a gesture, action, or sound.
"hold your fire until I signal"