Not that I think this hasn’t been done before, but I adapted highway shields in scalable vector graphics format from http://commons.wikimedia.org/wiki/Category:Highway_shield_blanks, since GeoServer can use SVG for symbolizing (we just need to put the SVG in the same directory as our SLDs, data_dir/styles):


Highway Shields in GeoServer
Now we’ll see if we can use pre-symbolized ones like on this page: http://commons.wikimedia.org/wiki/U.S._Route_shields
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