Personally, when handwriting, I got in the habit of striking a hyphen through the number "7" to disambuate against a possible number "1". Likewise, I'd strike through the letter "Z" to disambiguate from the number "2", and a diagonal strike through the number "0" to differentiate from the letter "O".
My handwriting is terrible, and it has saved me a lot of grief over the years, but especially in my engineering courses in college.
"Oh, you had ones? We had to use the letter ell."
For 7, just make the top long and the slash slanty. Don't do that for 1.
For Z, give the top a very slight curve, and optionally do the same for the bottom. That is, bend the middle of the line in toward the center of the letter. It might be enough to just imagine doing this, so that you don't end up with a curve going the other way. Give the 2 a proper curve instead of a sharp corner, and it will look different.
>in Japan, Korea and Taiwan 7 is written as ① in the illustration to the right. [1]
My handwriting also makes it hard to distinguish q from 9 in a situation where the baseline isn't clear.
I like and use your solutions, but the problem is that, if the reader doesn't know about them and doesn't have the other candidates to compare, a '1', a '2', or an 'O' has no visible mark to indicate that it's not a '7', a 'Z', or an '0'—that is, they are identified by missing, not additional, information. (I don't know any good solution, though.)
You: Yeah, Al here is our resident Network engineer. Go ahead and ask him a question.
Investor: So do you use any kind of drop-out or just as-is?
Al: Yeah, we don't have too much packet-los-
You: OK Moving along...