The Medieval Latin abbreviation for Canterbury (Cantuaria), used instead of his surname in the signature of an Archbishop of Canterbury. For example, the previous incumbent, Dr George Carey, would sign George Cantuar.
Likewise the Archbishop of York signs Ebor instead of his surname, from the Latin Eboracum. Several bishops also have distinctive Latin signatures, such as Roffen for the Bishop of Rochester (in Kent).
Not to be confused with Cantab, the Latin abbreviation for Cambridge as used in university degrees.