In a book called "Mustang, the Next Generation" (McClurg), SN-95 was listed as the internal Ford designation for the FOX-4 (or revised Fox) platform. The 'S' was for 'speciality', Ford-speak for the Mustang's market segment, and 'N' for North America, the geography indicator of the people responsible for its engineering. The '95' was a program sequence number.
the SN95's are the ones after the Foxes (our cars)...they ran from 1994 until 1998. If you wanna know what one looks like then go to the SN95 forum and look at some pics...you've seen them, they're not a special model or anything uncommon
Alternately, SN might stand for "StangNet" or "Screen Name."