My question is how to communicate this bounty in a way that the local rural busybodies would understand? Maybe a public key posted on Craigslist, Facebook Marketplace, etc, with instructions on how to verify the quantity?
First, sorry about your truck.
I think that you can make local bounty advertised in newspapers, local media and most popular websites, and state that reward can be paid in Bitcoin along with fiat currency.
You know what is popular in your area, offline and online, so you can make your own bounty posters and put them all around for everyone to see.
It's possible that f you choose only Bitcoin for payment you may get rejection from skilled hillbillies who are anti-bitcoin.
If I do this effectively, it could generate an army of motivated hillbillies scouring the countryside and tapping into their network of friends, family, co-workers, and I recover the truck. If I do it incorrectly, they won’t understand what the hell I am talking about or I inspire a $5 wrench attack!!
You can't make totally anonymous bounty because you have to post image of your track with license plate, but you can inform local police and authorities and put Bitcoin in some multisig, so that you can't be attacked so easy.
I think it's even possible to hire some Bitcoin trust to hold bitcoin with you as third party, and they could guarantee bounty payment if truck is recovered.