mawguy, on the hottest summer days here in the Murder Mitten I wear shorts with a 5" full underlug 629 (read 3 lb. gun) IWB at 3:30, a 24 oz. 2 1/4" Taurus 605 .357 in the weakside front pocket, a reload for both and a NAA .22 mag Black Widow as a final BUG in the strong side front pocket. Of course I use the best holsters (Fist 1A kydex/leather hybrid for the 629 and a Mika pocket holster for the Taurus) and a dual layer bullhide belt from
www.thebeltman.net . Provided you have no health issues precluding it, you can carry whatever you want if you're willing to deal with some inconvenience and dress around the gun/s. Busy pattern button down shirts with heavier fabric that are slightly big are my preference. I'm carrying a total of about five pounds of artillery, so I'll guess that a Sigma is easily doable with the right set up provided you have no health issues.
Last, but not least, I don't mean to sound patronizing. I don't know if you are an experienced carrier or not.