Generally that's != or it could be <>.
A != B
A <> B
Both are "A is not equal to B" but the first is more common.
EDIT:
the symbols above are used in programming, but in more simple mathematics the symbol is a ( =/= ) where an equal symbol ( = ) is slashed.
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Columbus
who invented equal to symbol
Put a slash through an equal sign.
An equal sign with a slash through it?
it is the equal sign = with the symbol ~ over it