1933 Anti-Spam Doorbell

Here's a great description of an anti-spam doorbell from 1933. A visitor
had to deposit a dime into a slot to make the doorbell ring. If the
homeowner appreciated the visit, he would return the dime. Otherwise,
the dime became the cost of disturbing the homeowner.
http://www.schneier.com/blog/archives/2007/05/1933_antispam_d.html