- " 'Hey, kid,' the old guy called as Marty walked past, 'can you thumb a hundred bucks to help save the clock tower?' He held out a silver box with the inscription 'Portable Thumb Unit'. / Marty hesitated. / 'It's an important piece of history,' the other guy added earnestly. The circular name patch over his pocket said his name was 'Terry'. "
- —From Back to the Future Part II by Craig Shaw Gardner (quote, page 49)
Portable thumb units were used in 2015 to collect donations and other funds where a person was unable to access a teller.
- Back to the Future Part II
- Back to the Future Part II novelization (First identified as Portable Thumb Unit)