Tell-tale bondage
From wipipedia.org

Tell-tale bondage is a bondage technique discussed by Jay Wiseman. It involves making some provision to tell if the captive has struggled or moved much; if he or she has, then some penalty can be exacted, such as being kept in bondage for longer or punished in some way.
Possibilities for the tell-tale include:
- Putting a stack of dishes on the captive's back (if he or she is face down).
- Putting a glass of water on the captive's back.
- Wrapping the captive in toilet paper, and seeing if it has torn.
- Making the captive press each finger of their left hand against the corresponding one of the right hand, with a coin between each pair of fingertips.
References
- Jay Wiseman, Jay Wiseman's Erotic Bondage Handbook, Greenery Press, 2000. ISBN 1890159131, p.312.