I tried out Signum Thunderstorm this week. Full bed, 53 lbs in my Youtek Radical Pro. The color is a bright purple, very distinctive. It is a 10-sided string that is twisted as well, but the edges are not as sharp as most textured poly's. Thunderstorm is very soft, comfortable, above average power for a poly, with decent spin (about the same as tornado). The spin is not as good as tour bite or alu power spin. The overall feel is similar to the Firestorm string.
I probably won't make this my main string, it's a bit too soft for me as I prefer crisper strings like Luxilon. Perhaps at 60 lbs it might work, but it's defintely worth a try for those that like soft arm-friendly polys.