Sometimes I write notes to myself. I do this because my short-term memory is imperfect. Call it a compensatory mechanism. Anyway, I've been doing this most of my life.
When I write notes to myself, I don't always necessarily want just anyone to be able to read them. Often the intended audience consists of exactly one person, me.
At some point I realized that, having studied a couple of foreign alphabets, I could write notes to myself in them, and most people wouldn't be able to easily read it, even if the actual words were entirely in English. Since English contains some phonemes that the foreign languages in question do not, I developed special conventions for representing those sounds, either by modifying existing letters with diacritical marks, or simply by taking a letter that normally represents a sound English doesn't use, and pressing it into service to represent an entirely different sound.
Of course, being the person that I am, I couldn't just leave it at that. After all, somebody might know the Greek alphabet. Somebody might know the Hebrew alphabet, for that matter. (This isn't as far-fetched as some might think. I know a handful of people who know both of those alphabets. In fact, I live in the same house with another such person.)
So naturally at some point I started mixing things up a bit. Being a bit of a glossophile, it was natural to learn several more writing systems and adopt some of the symbols from those. Some of the letters were too complex and took too long to write, so I simplified them by leaving off parts I deemed unimportant. At some point I changed my writing direction... and so it goes.
The note in the picture is a good example of the kind of thing I do now. (This particular note doesn't contain anything private, so if you're thinking of trying to decipher it, feel free, although you run the risk of being labeled a linguistics geek.)
Why am I sharing this? I have no idea. Maybe it's a feeler: am I really the only person who does this sort of thing?