Nothing signals “keep out” to potential readers more than a cipher, shorthand system, or code. Since the earliest years of the genre, writers have guarded their diaries with barriers—whether on every page, or only in selected entries—by using abbreviation, elements from other languages or alphabets, and symbols.

These codes don’t just make the diary challenging to read; in some cases they may render it invisible. During the Second World War Donald Hill, a British pilot held in a Japanese prisoner of war camp, disguised his diary as a mathematical grid that looked like a multiplication table.

Beatrix Potter, who later wrote the famous “Peter Rabbit” series of children’s books, kept a childhood diary written in a code she invented. In its pages she could record her frustrations with the social restrictions placed upon privileged young girls in Victorian England, without fear that her mother would punish her for expressing such inappropriate views.

Anne Lister, whose bold and rakish life was recently made famous in the “Gentleman Jack” BBC television series, kept a 19th-century diary even more voluminous than that of Samuel Pepys. Lister encoded the diary in what she called her “crypt hand,” a personal cipher based on letters of the Greek alphabet and other symbols. She devised the code in her early teen years to communicate secretly with her first love, a girl she met in boarding school.

Other examples abound. Pepys himself used a secretarial shorthand system to keep his diary safe from casual prying eyes; he added further layers of opacity by translating the more graphic details of his sexual exploits into a school-boyish mélange of Italian, Spanish, and French words. While this move probably wouldn’t do much to hide unfaithful behavior from his (French-born) wife, scholars have speculated that the naughty spice of foreign words may have enhanced Pepys’ own enjoyment of the memories upon re-reading.

Diaries kept entirely in code can prove nearly as cumbersome to generate as to read, and people wishing to conceal a whole diary nowadays have plenty of options for password protection and software encryption to keep the whole thing secret. But even pen-and-paper diarists can boost their level of privacy at special moments with a light touch of coding—perhaps by recounting events in indirect or elliptical language, inserting a symbol, or leaving strategic gaps.

Betty Jane Wylie, in her book Reading Between the Lines, points out that many diaries, especially those kept by women, “have a code of their own—subtle hints, ellipses, or deliberate omissions that force us to speculate or make educated guesses” (p. 26). While it’s relatively easy for the writer herself to recall the full story with help from her diary’s hints, or to fill in the omitted material based on the content of her memories, those readers who are farther away in time and not directly acquainted with the writer may never be able to crack the code.

In this way, the writer restricts a thorough reading of the diary to her own future self and to those close to her, who already know enough to fill in the gaps. As for strangers, only those who care enough to pursue the clues and conduct research will prevail: “Reading between the lines, rereading after other facts are revealed, breaking the diarist’s code, and perceiving other facts or contrary emotions with hindsight or with outside knowledge of her life and times, the reader begins to feel like a detective” (Wylie, 27). Even more, the reader begins to emulate a family member or close friend of the diarist, thus earning the right of access to the diary. (I’m indebted to Kaitlyn Goss-Peirce for this last insight.)

Based on her study of midwestern diaries, Suzanne Bunkers found that when a diary speaks evasively—or even remains silent—about something emotionally charged, like a taboo subject, the writer may in fact be expressing something very difficult in the only way possible. Such evasions and silences constitute “encoding” because they attempt to “transmit a message in an oblique rather than direct manner” (“Midwestern Diaries,” 194): “Indirection, contradiction, deviation, and silences” are paradoxical ways “of breaking silences, that is, of finding ways in which to speak” [italics added].

Arthur Ponsonby in his classic English Diaries (1923) is referring to material censored by an editor when he grumbles that “stars, blanks, initial and dashes are often very annoying and tantalizing to the reader.” The use of symbols, gaps, and abbreviations can also serve the diary’s original writer when they wish to track something in their lives that they prefer not to spell out. They may be summarizing material that honestly means more to the diary-keeper than it would to any future readers and that might be dull to read about in repeated detail, such as the current state of their digestive system, the day’s weather, or how often during a given period they paused to pray. In some cases, readers have nonetheless been intrigued enough to make extensive efforts to devise a legend and find what was hidden behind those encoded marks.

For the contemporary journal-writer the option to encode parts of a diary may offer a useful tool—one that has earned a place in the diary tradition. When an experience, topic, emotion, or relationship feels uncomfortable or even perilous to discuss explicitly, it can still find a place in the diary if noted indirectly, in disguise, or in a fragmentary way. Include just enough information to jog the memory and preserve what matters to the writer’s ongoing life. Ingenious use of codes can minimize the risks of betraying privacy or planting a landmine that others (such as the writer’s descendants) could trip over in the near or distant future.