Answer:
   
   The "qetzatzah ceremony" is described in the Jerusalem Talmud
   (Yerushalmi Kiddushin Chap. 1 and Midrash Ruth Rabba), and also
   appears in the Babylonian Talmud (the Talmud referred to when no
   adjective is used) at Kesuvos 28b. In general, it is a means of
   effecting a deal. For example, the Malbim (a 19th cent commentator)
   mentions it when writing on the book of Ruth. Ruth 4:8 says "that
   [handing someone your shoe] was the contract in Israel." Malbim notes
   that between the time of the story and the time of its writing, the
   standard means was changed to ketzatzah. Both are still valid today,
   the comment was about a shift in popularity, not validity.
   
   Ketzatzah involes breaking a barrel of fruit in the middle of the
   street and then making a formal announcement. An example of its use is
   a ceremony used to publicize a family's disapproval of the lineage or
   sexual history of someone marrying to one of their offspring. The
   family would revoke the child's right to inherit. To formalize this
   transfer, ketzatzah was performed announcing (translation from the
   Talmud): Hear our brothers Israel! Our brother so-and-so married a
   woman of improper lineage. We are afraid that our seed will be mixed
   with his. Come take some fruit as a rememberance, so our seeds will
   not get mixed.
   
   According to the Malbim, the point of ketzatzah is to do something
   that would make an impression not only on the adult witnesses, but on
   the children as well. Ketzatzah was used to keep the memory of
   something alive as long as possible.