And of course the
colored highway shields also became non-standard, again thanks to the MUTCD.
(More
here, and incidentally, this site also has information on
the Allegheny County Belt System, a local "we're too cheap to build a beltway" approach to getting people around the county. Note that the upper right corner of the Orange Belt enters Westmoreland County, briefly!)
And then there werethe pre-numbering routes, the most famous of which was the
Lincoln Highway.
My county has actually
posted historic Lincoln Highway signs along the roads which were the old Lincoln Highway (e.g. not the current US30 bypasses of Greensburg, Latrobe and Ligonier).