I'm thinking it's a 2910. Might not be.
Here is a Whelen 2X10 in McKinney TX. I know the signal, and I have heard the name so many times, but it's just not coming to me. It's at the tip of ym tongue, but won't come out.
http://www.youtube.com/watch?v=eckoGpla ... re=feedlik
Edit: I'm thinking it's called the "Best Possible Protection" signal.