Ryder Carroll suggests using the symbol "=" as a way of logging your feelings or moods within your bullet journal.

https://bulletjournal.com/blogs/bulletjournalist/how-to-improve-focus-using-a-bullet-journal

https://patrickrhone.com/dashplus/

referenced via Simon Woods at micro.camp https://hypothes.is/a/_GvLrPczEe2T-tfEqnLNhw

https://patrickrhone.com/2014/03/28/extending-dashplus/

Read archived version at https://web.archive.org/web/20230128105827/https://patrickrhone.com/2014/03/28/extending-dashplus/ Rhone's website was down today??

Shorthand notations or symbols in one's notes can be used to provide help in structuring arguments. Small indicators like "see: x", "see also: y", or "but see: z" can be used for adding supporting, comparison, or contradictory material respectively.

reply to stjeromeslibido at https://www.reddit.com/r/Zettelkasten/comments/10qw4l5/comment/j6x52ce/?utm_source=reddit&utm_medium=web2x&context=3

Luhmann often used the shorthand of red numbers to indicate a link to nearby card in the current branch/stem, which Scott Scheper calls "stemlinks" in Antinet Zettelkasten (2022) p234. So, for example, on card ZKII 9/8 there is a red "1" which indicates the branching card ZKII 9/8,1. Scott uses a more computer science oriented notation of "/1" to indicate this as if he were traversing up or down a folder structure. Since there isn't really a (useful) idea of a root or home folder, and one wouldn't often want to refer to their zettelkasten itself, one might consider using the solidus "/" to indicate the current card? I personally do this, but not very frequently, though I might do it more often with respect to indicating argumentation within and among other cards.

Some languages have location/proximity identifiers or markers (similar to here/there/over there). I'll sometimes use the Japanese markers (ko-so-a-do) as shorthand to provide rough approximation of idea relationships particularly when I have open questions. (example: kore, sore, are, dore -> this one, that one, that one over there, which one?) Many ideas are marked あ to indicate "just out of reach" or "needs additional thought". When ideas are adjacent or nearby, but by happenstance are relatively far away within my ZK (with respect to physical card distance in the box) they'll be pre-pended like こ/510/4b/3 (aka "ko"/510/4b/3).

reply to u/stjeromeslibido at https://www.reddit.com/r/Zettelkasten/comments/10qw4l5/are_there_symbols_for_supported_by_or/

In addition to the other excellent suggestions, I don't think you'll find anything specific that that was used historically for these, but there are certainly lots of old annotation symbols you might be able to co-opt for your personal use.

Evina Steinova has a great free cheat sheet list of annotation symbols: The Most Common Annotation Symbols in Early Medieval Western Manuscripts (a cheat sheet).

More of this rabbit hole:

• Steinová, Evina. Notam Superponere Studui: The Use of Annotation Symbols in the Early Middle Ages. Brepols, 2019.
• Cappelli, Adriano. The Elements of Abbreviation in Medieval Latin Paleography. University of Kansas Libr., 1984.
• Coulson, Frank, and Robert Babcock. The Oxford Handbook of Latin Palaeography. Oxford University Press, 2020.
• Lindsay, W. M. Notae Latinae. Cambridge University Press, 2013. https://archive.org/download/notaelatinaeacco00lindrich/notaelatinaeacco00lindrich.pdf.
• Bains, Doris. A Supplement to Notae Latinae (Abbreviations in Latin Mss. of 850 to 1050 A.D.). Cambridge [England] University Press, 1936. http://archive.org/details/supplementtonota0000bain.

(Nota bene: most of my brief research here only extends to Western traditions, primarily in Latin and Greek. Obviously other languages and eras will have potential ideas as well.)

Tironian shorthand may have something you could repurpose as well: https://en.wikipedia.org/wiki/Tironian_notes

Some may find the auxiliary signs of the Universal Decimal Classification useful for some of these sorts of notations for conjoining ideas.

Given the past history of these sorts of symbols and their uses, perhaps it might be useful for us all to aggregate a list of common ones we all use as a means of re-standardizing some of them in modern contexts? Which ones does everyone use?

Here are some I commonly use:

Often for quotations, citations, and provenance of ideas, I'll use Maria Popova and Tina Roth Eisenberg's Curator's Code:

• ᔥ for "via" to denote a direct quotation/source— something found elsewhere and written with little or no modification or elaboration (reformulation notes)
• ↬ for "hat tip" to stand for indirect discovery — something for which you got the idea at a source, but modified or elaborated on significantly (inspiration by a source, but which needn't be cited)

Occasionally I'll use a few nanoformats, from the microblogging space, particularly

• L: to indicate location

For mathematical proofs, in addition to their usual meanings, I'll use two symbols to separate biconditionals (necessary/sufficient conditions)

• (⇒) as a heading for the "if" portion of the proof
• (⇐) for the "only if" portion

Some historians may write 19c to indicate 19th Century, often I'll abbreviate using Roman numerals instead, so "XIX".

Occasionally, I'll also throw drolleries or other symbols into my margins to indicate idiosyncratic things that may only mean something specifically to me. This follows in the medieval traditions of the ars memoria, some of which are suggested in Cornwell, Hilarie, and James Cornwell. Saints, Signs, and Symbols: The Symbolic Language of Christian Art 3rd Edition. Church Publishing, Inc., 2009. The modern day equivalent of this might be the use of emoji with slang meanings or 1337 (leet) speak.

https://mittelalter.hypotheses.org/22292

https://en.wikipedia.org/wiki/List_of_logic_symbols