In the collectibles world, this durable antique art form is a perfect example of the old "forest for the trees" maxim. Despite their bold designs and colors, only recently have collectors caught on to the value of these antiques of Americana. And the hunt is on. Once posted in every corner of the nation, this durable art form has yet to shed its luster. At the turn of the century, porcelain enamel signs became a standard form of advertising, and they...