Buongiorno Zis!
I've enlarged the photo to get a closer look but the image remains a little blurred however .. it appears to me to be the emblem of the Air Squadron.
Can't say much about the Squadron other than Ken McAlpine was a member (and which is probably why it was painted on BBSI) and also that my late-godfather was friends with some of their members including Tony Everard and Johnny Moss.