An X for a halo?  Presumably it's the tail end of the ichthys symbol ("sign of the fish") of Christianity, but we've never before encountered it this way (we have gaps!)  The red "64" sticker seems like a sun that Jesus is warding off.  The sun and the Son.  In mathematics, 64 is known as a "centered triangular number" (symbolic here of the Holy Trinity?)  Of course, there are 64 demons in the Dictionnaire Infernal, and 64 hexagrams in the I Ching, and 64 squares on a chess board, so there are many (unsatisfactory) ways to interpret the cover of Sacred Heart's 1964 yearbook.