As a proud (and also 260Euro less rich) Signature Edition owner, the Stealth models all come with super high detailed carbon texture. It's incredible how detailed those high res carbon texture are compared to anything else in game. Just click on enlarge and you can see what I mean.
Another nice side effect. Those cars get easier dirty, their rigidity and engine overhaul repair always only cost 500credits (instead of 500000) and they come with a standard hp boost that even tops the usual oil change hp boost and also will have more hp when maxed tuned.
They're just bad ass.