The Sigma was a high-end, luxury version of the 5th generation Galant. Sold from 1988-90 in the U.S., the Sigma went head to head with Toyota Cressida, Acura Legend, and Mazda 929. The Sigma featured modern styling, a V6 engine, and a host of '80s Japanese-luxury goodies. Today, like all old Mitsubishis, Sigmas are rare, especially compared to its competition.
On a side note, I apologize for the bright-sun shots. We have had just a handful of cloudy days since May, which means that the few cars I do end up taking pictures of look like this.