Only if you identify them by make, model etc, and that includes the words you use to market them and any identifying names on the models, including but not exclusively restricted to decals.
It's a gray area, but the trademark might also apply to just the basic shape. A VW Beetle would be obvious, and even a vintage Mustang or Corvette look like nothing else.
So to be absolutely safe, you get a licensing agreement for anything you want to copy. The old model makers like Aurora, Revell and the like always did.