I sometimes name FileMaker Custom Functions with a special character prefix so that when I see them in calculations there is a visual difference from:
~ (Let Function variables)
Table Occurrence Names
Built in FileMaker Functions
Plugin functions (which notably use prefixes as well)
As far as I know, FileMaker Custom Functions are not called by external technologies and therefore we can safely use characters in the name that we would want to avoid in, for example, Script Names, Field Names, etc.
Using a prefix also facilitates type ahead as a single keystroke separates Custom Functions from built in FileMaker Functions
For my part i have two different syntaxes, one for functions I use very often and one for the rest. I am an old school, low level, software developer, so I have a minimalistic approach that I don't see in most others code examples. (Started with Assembler and Forth in the 1990's).
Anyhow, these screen dumps should be self explanatory, and the naming convention makes it very easy for me to remember. Something that is important for me, since may standard library currently contains 483 custom function.
With the name space approach I can easily spot them in my calculation, and with the "look ahead(?)" i just start typing "num." to see a list of all my functions concerning numerals. (I also use MBS plugin extensively, and love the Syntax colorization).
So first are the often used CF's, and then some random screen shots from the list.
(The parameter "setup" is a map data structure that makes it easy for me to add more options to a them).