[2001 ZTS]

I know about the various "turn signal mirrors" out there but I think these may actually be covers? From the same site, and using the same picture, the listing for the 1994+ Mustang has:

TURN SIGNAL MIRROR COVERS
Available unpainted or in carbon fiber look, these euro style turn signal mirror covers fit 1994-2004 Mustangs. Covers snap over your stock mirrors and come with the wiring to tap into your turn signals. Clear lenses add to that Euro look. Sold in pairs.

It also looks like Morette may be as well (slow site):

http://www.morette.com/mirrors/MainMirrors.htm

Not sure if the Morettes would ever fit our cars though.