Alternatives I considered to the negative circled dingbats:

Alternative: Writing the numbers upside-down.
Rejected because: I’d have to use CSS to represent that on-screen, and then this page wouldn’t work in plain text. (Not that this page works well in plain text to begin with.)

Alternative: Putting an overline over negative digits.
Rejected because: Again, CSS. Although this is the method I use when I’m writing by hand.

Alternative: Using the letters A through H for -1 through -8.
Rejected because: Should A be -1 or -8? It would be weird to count up and go “7, 8, 9, 1H, 1G, 1F”, but it would also be weird to be counting backwards and go “3, 2, 1, 0, H, G, F...” Also, I briefly tried this when handwriting and I had to keep stopping to remember which letter represented which digit.