But they are about to become a thing of the past.

The department is retiring handwritten memo books by Feb. 17 in a transition to a digital version — an app on officers’ department-issued iPhones. Instead of making entries by hand, whether with flowery script from ink-dipped pens in Victorian-era New York or ballpoints today, officers will type in their notes, which the app will send to a department database.

The transition represents a major shift in the way the department regards this daily record keeping by more than 30,000 of its uniformed members, and it will vastly revamp how the department can access memo book information.

In addition to the books’ historical importance, entries can become important legal documents. Department officials say the transition will help eliminate possible abuses, such as faking entries, and having to sort through indecipherable handwriting.

After arrests, officers have long turned over relevant entries — on crime scenes and on statements made by suspects or witnesses, for example — to prosecutors, and were expected to bring their books to court if they were called to testify.

The memo books largely stayed with the officers, who were required to safeguard them even after retirement, since the books could be subpoenaed as evidence in future criminal, civil and departmental trials.