Lyn,
The coat -of-arms was the same in the Grammar era, except that the letters at the base were SGS rather than SSS. The four quarters represent the four "houses". When you joined the school you were allocated to one of them. They were Bright, Boulton, Kendrick and Priestley. I was in Priestly and wore a white badge. I think the symbol on the coat-of-arms was the crossed keys. Struggling with ancient memory, but I think Bright was the sheaf (yellow badge), Boulton was a blue badge and Kendrick was green. Can't remember which had what symbol though.
Cheers,
Stan