Coon droppings are usually a sort of "pile", most times left on a log, root, rock, or other low structure. It kinda has the consistancy of a mild case of the squirts, and a lot of times contains various seeds, and other matter.
Coyote droppings look pretty much like regular old dog droppings. They tend to be kinda pointed on the ends, and most times have a good bit of animal hair in them. At times they will also contain bits of bone, and seeds.
It's actually pretty hard to confuse the two if you've had any experience observing them.