In the old days, a 'nose' was a name for a special board or tag, on which special marks were put and, thus, marked, for example, debts, days of the week, purchases, etc. In general, everything that needed to be memorized you can "зарубить на носу" (‘zarubyt na nosu’) or ‘nail it on the nose’ . You could say it was an ancient version of a calendar with reminders, a daily planner and even a calculator. Often, the plaque was divided in half: one half was kept by the debtor, the other half by the lender. And, for "authorization", the halves were matched, so that the creditor knew that the debt was being settled for that particular debt.