The bank was where Dr. Emmett Brown placed his valuable comic books in 2015, under the alias "Leroy Brown".
Doc had purchased ten copies of Action Comics Issue #1 in 1938 with a silver dollar heirloom to sell in 2015, as he discovered that they had become a valuable commodity. He sold one issue to purchase a hover conversion and a Mr. Fusion reactor to use on his DeLorean time machine, to purchase a false identity, to get a rejuvenation treatment and to place his dog, Einstein, in a suspended animation kennel. He then placed the other nine copies of the comic book in the safety deposit box at the bank.
When Doc accidentally traveled from 1893 to 2035 in the steam time car, instead of 2015, he tried to withdraw one of his comic books. However, the bank teller scanned him and noticed that his genetic age did not match the age that he should have been if he had aged 20 years since he set up the bank account in 2015. She called the police, as she assumed it to be a case of identity theft, and thought that Doc was merely a cheap clone.