I am sure that the high decible signature is sufficient warning..
I'm not. Considering the speed at which turbine powered aircraft fly (I'm taking piston engines out of the picture because usually they're small and more maneuverable) engine sound is not heard until probably a few seconds from impact.
Consider for example the USAir birdstrike:
YouTube - NTSB Animation Flight 1549 Hudson River Landing US Airways
The aircraft was accelerating from 210 to 218 knots when the birdstrike event happened. And from there, we could only expect speeds to increase, and having numerous reports of birdstrikes in higher flight levels, we can only assume the speed was much higher.
So the "high decible" doesn't apply here.
A recent NTSB Safety Recommendation was issued after the USAir birdstrike:
Work with the U.S. Department of Agriculture to develop and
implement innovative technologies that can be installed on
aircraft that would reduce the likelihood of a bird strike.
(A-10-76)
Which ever other serious technologies you can think of, please share. Still on animal behavior, to make one's presence aware to others, the first method used is via sound.
However, the method will fall behind as speed increases. Maybe a device that would produce small sonic booms that would travel ahead of the aircraft giving an early warning to a potential hazard?