Did CF Martin sign the wood brace of any 1970's D 28's?

C.F. Martin did not typically sign the wood braces of their Guitars, including the D-28 models from the 1970s. The practice of signing braces became more common in later years but was not standard during that decade. Therefore, it's unlikely to find a signed brace in a 1970s D-28. If you have a specific guitar in mind, it's best to consult detailed records or an expert for verification.