I have grapheme-colour synesthesia (a strong, consistent association of letters with colors). Back in college, I wrote an article for my campus newspaper describing synethesia, and I included the full mapping of letter-color associations in a sidebar.
I rediscovered that clip about ten years later and, without looking at the sidebar, jotted down all of my letter-color associations. They were remarkably consistent!
I tend to also associate letters and numbers with a particular gender, even though the concept of a grammatical gender doesn't exist in English. There isn't anything about the shape of the letters or any similar pattern that explains why I associate "H" with female but "I" with male. I'm not sure that counts as synesthesia, though.
I rediscovered that clip about ten years later and, without looking at the sidebar, jotted down all of my letter-color associations. They were remarkably consistent!
I tend to also associate letters and numbers with a particular gender, even though the concept of a grammatical gender doesn't exist in English. There isn't anything about the shape of the letters or any similar pattern that explains why I associate "H" with female but "I" with male. I'm not sure that counts as synesthesia, though.