I adore these Go Green stamps from the USPS. Not only do they show simple green acts, but they're also Forever Stamps. While all of those things are fabulous, perhaps my favorite thing is that you can get these (or any other) stamps ordered to your mail box! It saves a trip to the post office & the accompanying emissions & only costs $1 for handling.
The $1 fee is applied no matter the size of the order, so it is advantageous to purchase multiple sheets at a time. For instance, I ordered $28 worth of stamps, paid the $1 handling fee, & saved the trip to the post office. Saved time & saved gas. Piece of cake.