They're just a bit rarer than pull tabs. It's a highway sign which (unless the local chapter is no longer around) was meant to stay put, and probably was removed by some kid who thought it would be a swell trophy. Although, presumably they might replace them if they were too worn, but I see worse ones still roadside, so...
Anyway, they do show up on eBay, though I'm not sure they should, and recent selling prices were 9.99 and $25 for one in freshly stolen condition.
that is a pretty old one (the "recently stolen from highway" ones..as someone put it...look nothing like that) - Im not sure if Ebay is the way to go...being a larger item....if I brought it to the flea market Id start at like...40..50 bucks...is it porcelain over metal?