If you noticed it ... well, they're supposed to look different - and catch your eyes sooner as well. The new signs are the first of their kind in South Carolina using the "Clearview" font. Being in the highway construction business, as well as doing quite a bit of graphic design, this kind of stuff interests me.
Since the inception of the Interstate Highway system in the 1950s, signs on Interstates, as well as large-sized signage on non-Interstate highways and freeways, has used variations of what was known as the Highway Gothic font. Thrown into service without any research into visibility, it was used first on signs where die-cut lettering was tacked onto steel signs, and then other more modern methods of construction.
Research found the Clearview font is cleaner, neater, allows more space for lettering in signs because of the narrower width of the text, and is easier to read - especially for older drivers - than the existing Highway Gothic font. The use of signs with this font received initial approval by the Federal Highway Administration in 2004, which is responsible for setting and maintaining standards for such things, and has shown up in a number of states.
These photos to the right give you a chance to compare and see for yourself the difference between Highway Gothic and Clearview (it might've helped if the signs were both in good condition, but I've noticed the difference when good-condition signs are replaced).
The installation of new signs using this font was a first in South Carolina, but it probably won't be the last.