To add my two cents to the many comments on D.Pitchon's posting -
I thought of the yarmulkahs in my dresser drawers about 2-3 years ago.
They had good information and I included all of it in my genealogy
However, the real treasure find was when my mother uncovered some
yarmulkahs and a lace handkerchief two months ago >from a fairly observant
part of the family with which we had lost contact. We learned what the
daughter's married name was as well as the B'nai Mitzvah date for the
twins. Although these events took place more than 35 years ago, the
information given enabled me to renew my search for these second
cousins with very promising results.
And, as to how long this practice has been going on?
My parents had plain white satin kipot printed with their names and the
date when they were married amonst 47 years ago.
Thanks for mentioning this good resouce to the group.
San Francisco, California