> I don't like the idea of a punctuation prefix as punctuation usually has a specific meaning somewhere and including it as the first character in a filename looks wrong.
So you don’t use dotfiles? ;)
I'm not convinced by "quicker to type" arguments as that's rarely the bottleneck, so I'm perfectly happy with using underscores in filenames and variables. I wouldn't use underscore as the beginning character of a filename unless it had a specific meaning to me (e.g. temporary files), so I'd be more inclined to use a two or three character prefix instead.
Nowadays, I tend to skip using a personal prefix and just try to name commands with a suitable verb in front (e.g. "backupMySQL") and ensure that there's no name collisions.