Here is an interesting excerpt from my property text book that reminded me of those heart shaped best-friends-forever necklaces that split into two pieces.
In the days before typewriters and carbon paper, and centuries before Xerox, lawyers were faced with the problem of providing duplicate copies of deeds in certain instances when both the grantor and grantee wanted a copy (for example, in case of a mortgage). They found the solution in an indenture. The deed was written out twice on a single sheet of parchment (usually made from sheepskin stretched, scraped, and scoured) and signed at the end of each copy by both grantor and grantee. The parchment was then cut into two pieces in an irregular line, leaving a sawtooth or indented edge. The two halves, forming two separate deeds, one for the grantor and one for the grantee, could be fitted together to show their genuineness.