Firearms may not be carried:
"any premises, except state owned rest areas or stops along the highways, where
notice that carrying a concealed handgun is prohibited by the posting of a
conspicuous notice, or statement by the person in legal possession or control
of the premises.
N.C. Gen. Stat. § 14-415.11(c)"
There is no mandated style or type of sign in NC. If they post it, ( even with cardboard and crayon) it is illegal to carry inside in NC. If it is posted and you enter, you are already breaking the law. You do not have to refuse to leave in order to be tresspassing. It only has to be in a place where it can be seen before you enter. If there is no sign and you enter, and are then told by someone in charge of the premises (owner or employee) that they don't allow firearms, you must then leave, or you are breaking the law.