55 D over S is a good one. I thought I had one but my old LCS guy said it looked like a D over D to him. Your title says 1950 D over S.
It is an early one. This is the third generation of ANACS certificate used from 1978 to 1981. They used this same type both before and after they started grading coins. This one was issued shortly before they began grading while they were still strictly an authentication company.