I recently purchased a 5' x 4' Mobilgas reflective highway sign. At the top, it says "Just Ahead." Under that is the shield with pegasus and "Mobilgas" and "Socony-Vacuum." I would like any information regarding dating and value, but I would also like any advice on how to clean it. The texture of the sign is very rough/sandy (I think because of the reflective coating) so I don't know if scrubbing or certain cleaners would damage this coating. Thank you for your help.

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