I was confused about the Trijicon and AmeriGlo references for the same sights. Turns out that AmeriGlo makes the metal sight housings, ships them to Trijicon who makes and installs the tritium tubes in the housings and ships them back to AmeriGlo who then sells them as AmeriGlo night sights. These may carry the Trijicon lable on the sights. Trijicon sells its own sights (which look suspiciously like AmeriGlo),
http://www.opticsplanet.net/trijicon-sa22-sigma-40-3-dot-front-rear-night-sight-set.html
I don't think AmeriGlo makes sights to fit the Sigma yet; here is a place that carries "PT" Sigma night sights.
Arizona Gun Runners - Sigma
These are almost half the cost of AmeriGlo/Trijicon or Meprolite sights, and you can get colors other than green for your rear sight.
Meprolight makes Tru-dot night sights for the "Smith and Weston" Sigma "Value" series. The "V" in the Sigma name stands for the stainless steel slide, not "Value". They have no white ring, so in daylight you may have to just use the tops of the iron sights, which is not necessarily a bad thing.
http://www.meprolight.com/default.a...itemid={3C4E58DE-C806-4093-9C1E-C60CA9AD5285}
Brownell's claims to have OEM S&W night sights for Sigma as well, last I checked they were out of stock and they list them as being for the Sigma 40V, not the VE and I don't know if it makes a difference.
Haven't used any of them, so I can't vouch for quality.
I'm buying an AmeriGlo/Trijicon (front sight only) for a Glock and will file the slide insert down to fit the Sigma 40VE. I don't want the rear night sight. In a self-defense situation you should only be seeing the front sight, and I don't go target shooting in the dark.
http://www.glockworld.com/item/42365_Ameriglo_Sights__Lasers_AMER_GL112_NIGHT_STS_ALL_.aspx