This is scheme where a card is given to a house owner on which he writes the name and address of a neighbour (or relative).   The card is shown (through a window) to tell any strange or odd looking visitor to contact the name on the card.

The idea is for the nominted person to accompany the stranger to the house owners house.   It is obvious that only genuine callers will make the effort to contact the neighbour.

This scheme has worked well in a trial area and is recommended for elderly people  living alone.