The Mark of the Cross
The old Danish laws made it obligatory upon those who could not write to affix their bomærke (house-mark); and the Russians required a mark, or a cross. The probable reason why the cross was always used in the Middle Ages in the testing of ecclesiastical charters was not only that it was a sacred symbol, but that Justinian had decreed it should have the strength of an oath.—B. Williams, F.S.A.; Archæologia, xxxvii. p. 384.
Sir Henry Spelman tells us that “The Saxons in their deeds observed no set forme, but used honest and perspicuous words to express the thing intended with all brevity, yet not wanting the essential parts of a deed: as the names of the donor and donee, the consideration, the certainty of the thing given, the limitation of the estate, the reservation if any were, and the names of the witnesses, which always were many, some for the one part, and some for the other. As for dating, it was not usual amongst them. Seals they used not at all, other than (the common seal of Christianity) the sign of the Cross, which they, and all nations following the Greek and Roman Church, accompted the most solemn and inviolable manner of confirming.”