I don't know either, maybe the "S̶t̶r̶i̶k̶e̶-̶t̶h̶r̶o̶u̶g̶h̶" letters :) It's UTF8
Discussion
Hahaha! I was referring to the fact that most clients don't display the edited version. The strike-through is very nice :)
I still don't understand the argument against edits. I only see people giving examples saying "this is why edits are bad" without giving reasons