>The right to use the easement. And drive in and out with loud music blaring or the engine revving at any time day or night is what I was referring to.

You could be right if this is a very strange easement that includes a proscribed right to place signage, in addition to a right-of-way. I highly doubt it. That said, easements do not give you a right to cause a nuisance with noise or litter. Putting aside common law nuisance, most Vermont municipalities have noise ordinances. If the neighbor retaliated in that way, they would be the only asshole in the situation, and could open themselves up to a civil stalking order.

All OP needs to do is return the sign and be friendly.