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The B4C is for the police package supplied by the manufacturer which it is include the SEO (Special Equipment Options) code. I would suggest that it can be used as extra information field like the 9C1 police package as well 
https://en.wikipedia.org/wiki/Chevrolet_Camaro#Third_generation_(1982–1992)
https://en.wikipedia.org/wiki/Chevrolet_Camaro#Fourth_generation_(1993–2002)
@Edit: I found more information in regarding to 9C1:
https://en.wikipedia.org/wiki/9C1_(Chevrolet_Police_package)
https://en.wikipedia.org/wiki/Chevrolet_Camaro#Third_generation_(1982–1992)
https://en.wikipedia.org/wiki/Chevrolet_Camaro#Fourth_generation_(1993–2002)
@Edit: I found more information in regarding to 9C1:
https://en.wikipedia.org/wiki/9C1_(Chevrolet_Police_package)