For reasons that seemed good to me, I was leafing through The Unicode Standard, Version 3.0 — 1,040 pages of character-set goodness — when I stumbled across this pair of characters on page 520:
- ≸ (U+2278) — neither less than nor greater than
- ≹ (U+2279) — neither greater than nor less than
It moves my soul that both of these exist.