I am a St.John (period, no space) and during my research, I have found all the variations of my last name, even within my tree. From birth certificates, to census', to death certificates, for the same person, there have been STJOHN, ST JOHN, ST. JOHN, and ST.JOHN. I haven't come across any SAINT JOHN's in my tree tree, but I've only gone back to the 1600's so far.