Anno Societatis (often abbreviated to "A.S.") is Latin for "(In/Of) the Year of the Society".
This is modeled on the modern practice of dating years since the birth of Jesus of Nazareth as "Anno Domini" ("A.D.", "In the Year of Our Lord"). In more recent times, "A.D." has been replaced with "C.E." (Common Era).
The S.C.A. was founded in May of 1966, therefore A.S. I runs from May 1966 to the end of April 1967.
Society years are usually written in Roman numerals. (I = one, V = five, X = ten, and L = fifty.) Common Era years are written in arabic numerals. (1966, 1967, 1968, etc).