I use to work for one of the primier Muzzlebrake companies and we tested them all.
They all worked and they all made noise. As far as one working better than the other, it was all perception and good sales presentation.
Those that had holes angled forward "seemed" quieter. They also "seemed" to not be as effective in reducing recoil.
Now what I take the meaning of sound signature is, is the ability to tell where the shot came from. They are very good for that. From down range they are very difficult to clearly identify where the shot came from.
If there is one on the market that I would recommend, it is the one from Jim Brockman.
http://www.brockmansrifles.com/mbrake.aspYou open it for shooting on the range with your earmuffs on, and you turn it off when hunting.
Nope, I didn't use to work for Brockman.