The flag of St John Ambulance has an eight-pointed St John cross and lions and unicorns. St John operates with this badge in England, Australia, many other Commonwealth nations and the US.
I have also seen photos of the flag of 'The Most Venerable Order of the Hospital of St John in Jerusalem' (which St John Ambulance is connected with) flying in Canberra and at Clerkenwell, England. It is the white cross on red (as the SMOM) with the Queen's Crest. If someone knows exactly what the Queen's Crest looks like, they might like to gif this flag too.
From the St John Ambulance Australia Cadet Manual 3rd edition:
The St John Ambulance Colour is the badge of the order, i.e., a white cross with gold lions and unicorns on the black field, with a 5 cm fringe of alternate black and white. It is carried on a 2.4 metre pole surmounted by the Badge of the Order in silver. The pole has black and white cords with tassels. The St John Ambulance Flag is the Badge of the Order, that is, a white cross with gold lions and unicorns on a black field. The Cadet Flag is the Badge of the Order, is a white cross with gold lions and unicorns on a black field, with a plain gold fringe. It is carried on a black 1.8 metre pole with a polished polehead and white cords and tassels. There should be no Divisional names nor other writing on any St John Ambulance or Cadet Flag. The Cadet Flag Party consists of three cadets, the senior cadet being the flag bearer and flanked in line on either side by the remaining two cadets.
Captions: "First Aid Flag (4' 6" x 3')" and "Lightweight polyester green flag with St. John Ambulance logo. Clean through cool polyester wash in washing machine. Leave to dry naturally. 137cm x 91cm."
It is a dark green rectangular flag bearing white words "FIRST AID" (no serifs) in the upper portion, the St John Ambulance circular seal in the lower hoist and a white couped cross in the lower fly.