Thanks to Stephen for this information.
If your digital speedometer constantly displays an 'S' in the space underneath the speed display, that indicates that at some point your speedometer module was replaced under service at the Ford dealer. There technically should be a sticker affixed inside your driver's door jamb to indicate this.
To remove the "S", you will need to remove the cluster from the car. Following the same general information used in the 199mph speedometer modification, along the same side of the board are several jumpers at W3 & W4 that can be removed or cut. These will permanently remove the "S" from your display. Then reinstall the speedometer and dash cluster to test. Enjoy!