I'll echo what Bernie and Matt said (and be careful...the statute above refers to
POSSESSING blue lights, not just display).
The only other one I could find was this:
http://www.ncleg.net/EnactedLegislat..._20-137.2.html
§ 20‑137.2. Operation of vehicles resembling law‑enforcement vehicles unlawful; punishment.
(a) It is unlawful for any person other than a law‑enforcement officer of the State or of any county, municipality, or other political subdivision thereof,
with the intent to impersonate a law‑enforcement officer, to operate any vehicle, which by its coloration, insignia, lettering, and blue or red light resembles a vehicle owned, possessed, or operated by any law‑enforcement agency.
(b) Violation of subsection (a) of this section is a Class 1 misdemeanor. (1979, c. 567, s. 1; 1993, c. 539, s. 362; 1994, Ex. Sess., c. 24, s. 14(c).)
Key words above in bold. I think you'd be fine with the decals covered, "Show Car" signage, etc. No crime if there's no ill-intent.