A short History of Letterboxing in North America.
Stamp the logbook with your personal stamp, then stamp your personal logbook with the box's stamp. Or vice versa. Or just sign the log if you don't have a stamp.
Local Letterboxes are listed here on LbNA's site and/or on the [other commercial site]. They show these others here in Kinderhook and Valatie:
Letterboxing seems to be Geocaching's older brother that's been around in some form over 100 years but didn't make it big. We've learned that online Letterboxing has many fewer participants, no volunteer reviewers, and therefore less self-policing.
Enjoy!
Way to go geo.duck on FTF!