Which preposition to use with martlets

from Occurrences 1%

Gates of wrought iron, with perhaps a martlet from the Byrd coat of arms above them, swung between tall pillars in the wall.

in Occurrences 1%

Your arms are a martlet in fess upon a field azure, and now that I think of it, the second daughter of your great-grand-father married the son of one of the La Noues of Andelys, which is one of our cadet branches.

Which preposition to use with  martlets