You really have to look under the hood. Starting in 93 or 94, the trunk lid insignia no longer differentiated between a "940" or "940Turbo", they all said "940".

Look for the presence of a turbocharger attached to the exhaust manifold on the passenger side of the engine compartment.

You can't really tell by the wheels, trim, etc., because by 94 or 95, the option and trim packages were all over the place.

My wife's 95 945T doesn't look like a turbo at all. The dealer replaced the black grille with the black/chrome grill just before we bought it, and it came with 15" steel wheels and hubcaps. Plus, it just says "940" on the tailgate, unlike my 91 944T, which had the black eggcrate grille, fogs between the grille and headlights, 16" "Hydra" alloys, and the "940Turbo" insignia on the trunk lid.