Keep my nose out of it?

Here's another thing that's bothering me. In our tiny village, we have this great little general store which stocks all kinds of random things and is dead handy in a pinch. In the morning the flatbed trucks line up outside as locals grab a coffee and an egg and bacon sandwich on the way to work, and round about now (6 o'clock) they stop off for pizza and other homemade Italian specials on their way home. But here's the thing: they all leave their engines running while they're in the store. I think this is partly a display of trust - most people up here don't lock their front doors, either - and it probably also serves a practical purpose - they like to leave the AC or heat on. But what a total waste of petrol. So how do I handle this?

I could a) keep my nose out of it (after all, in the grand scale how much damage is this really doing?) but per my previous post, this is a bit lame; b) go and ask people nicely to to turn their engines off; the catches here being that I don't know how many of them have guns and I can't imagine these rugged outdoorsy folk would be best pleased to have a prim English girl telling them how to run their lives or c) speak to the store owner about possibly putting a sign up saying 'please, no idling', the problem here being that I don't want to alienate them (the previous owner of our house did and as a result became a pariah in the village - not to mention what will happen when teatime next rolls round and I realize I'm out of milk?). Well, for now I'll just sit here and kvetch about it but please leave comments, below, as to what you reckon I should do. Yours, Busybody Williams.