The Saleen S-281 is a variant introuced between the 4th and 5th generations of Ford Mustang which was produced by the American manufacturer Saleen, Inc. By 2005, Saleen departed from being a company of modifying existing Ford Mustangs as well as various other Ford automobiles, and now became an official Original equipment manufacturer. This was easily distinguishable with the body work designed by Phil Frank on the S-281's as well as the various other models offered by Saleen.
Previously referred to as Saleen Mustang, Saleen now introduced a model designation based on the Cubic Inch Displacement (CID) of the engine, now referring the car as Saleen 281 CID, or simply S-281. Any distinguishable options purchased by the customer is indicated with a suffix added after the 281, designating its difference.
Source: Wikipedia (original)