And they did so repeatedly. In another ad featuring that same car, you get a view of the special license plate they had made up for the car with a stylized "S":




And it wasn't just with early models. Click on red ad in the thumbnail below for an example of this late 70s special "S" license plate (and "S-type" terminology in the beginning of the third paragraph) being used.

And I'm not done! Here's an ad of an '89 model still being called this (see wording in the 2nd paragraph):