Cross with a snake. Perhaps I shouldn’t have taken it out of its context. According to Day: “The symbol of a bridge with three arches is by no means rare”. He gives an example of an “Ark Mariner” warrant with an arch with a cross and serpent on it and a Red Cross Certificate with similar symbolism.
Also: “Bro. Songhurst, in reply to my enquiry, considered that the Kirkwall illustration might perhaps refer to the degree of Red Cross of Babylon. I had suggested that the two figures on the centre arch were performing an act of reconciliation between the old covenant, represented by the Ten Commandments and the Brazen Serpent on the right, with the new covenant, represented by the Lamb and the Book of the Gospels on the left. Bro. Songhurst questioned my idea of ” reconciliation,” and suggested that the figures might be lifting up their hands in hostility. I had based my reconciliation interpretation more on the fact that the figures appear to be kneeling.”
Would this be a repetition of another snake on a cross a bit higher up on the same panel?
More about the Brazen Serpent here.