Keystone shaped signs mark entrances to many Pennsylvania towns.

I see York city is restoring its Keystone markers, those familiar keystone with a rectangle signs that tell you the town you are entering, where its name came from and how many miles down the road to another town. Good for the city–every bit helps in first impressions.
There is a lengthy history of the Keystone markers on the Keystone Marker Trust web site. It also has helpful information for communities who want to restore their markers. Replacement markers, made in Pennsylvania, are also available, but restoration is much more economical if the marker isn’t completely missing.
The Keystone markers, as you can read on their historical information page, began as a Pennsylvania Transportation Department (predecessor of PennDOT) project in the 1920s, when more and more people were taking to the highways. The Keystone Marker Trust is a separate non-profit organization and is not connected with the Pennsylvania Historical and Museum Commission’s historical marker program.
One little thing–founding dates on the signs should be taken with a hefty grain of salt, as the Red Lion sign above illustrates. Red Lion was founded in 1880, from parts of York Township (founded 1753) and Windsor Township (founded 1758). York County was part of Lancaster County until 1749, and most York County Townships roots go back to Hellam Township, which was laid out in 1739, while still part of Lancaster County. The 1736 date might have picked up, as is suggested on the Keystone Marker Trust web site, because that is the date of the treaty between the Indians and Penn proprietors that officially allowed settlement on the west side of the Susquehanna River.