Legal Question in Criminal Law in North Carolina

Can they? Sure. And there is really no reason for the other property owners to care except for maybe they think the sign is ugly or tacky. However, the question you likely want answered is whether it is legal and who has to abide by the sign. Assuming this is an easement for the property owners and not a public easement, the answer to that is yes, it is legal and the one property owner doesn't need permission from the other property owners to post the sign to protect their interest. However, the no trespassing sign obviously would not apply to other property owners who are entitled to use the easement or anyone the other property owners gave specific permission to use the easement. So the one property owner could not use the sign to keep out anyone the other property owners may give permission to use the easement.