The "Sigma" is found in several flavors. F, C, V, E, VE. It seems the triggers got worse the further along they went. I have a .40 C and a 9 V. The V has a noticibly rougher/heavier trigger than the C. I have handled some VE's that had REALLY CRAPPY triggers.
The really early F and C models iin .40 had problems with chambering anything but "perfect" ammo. These were the first guns made in .40 S&W and the engineers goofed on the tolerances. S&W replaced the barrels on these (and fired the engineer responsible). Serial # prefixes PAA and PAB were affected by this.
Because they have very light weight frames they can be prone to limp wristing. IMO, 95% of the reliability issues can be solved with a firm grip. The problem is they are marketed to novice shooters who do not know how to properly grip an auto loading pistol.