The term “Celtic” has been sometimes used in Society blazons to indicate a style of depiction: e.g., a “Celtic hound” would be a hound as drawn in the Book of Kells. The term is thus a direction to the artist, not a variant of type, and carries no heraldic difference; indeed, it’s more commonly not blazoned. Moreover, a charge drawn too strongly in the Kells style may be rendered unidentifiable, and so unacceptable. Two exceptions are the Celtic cross and the Celtic harp.
Sabia Gunnhild Hunang bears: Gules, a Celtic hawk statant close reguardant Or. [The hawk is drawn as in the Lindisfarne Gospels.]