Symbol for "Unicode mess"

Question

I'm looking for a symbol which meaning is "things that should not be in Unicode".

Does such Unicode character exist (yet)? If yes, what's the codepoint? If not, how do I propose for it?

Answer 1

The REPLACEMENT CHARACTER (U+FFFD) � should be used for characters that can't be represented. From the link:

used to replace an incoming character whose value is unknown or unrepresentable in Unicode