Wikipedia says:
Not equal
The symbol used to denote inequation — when items are not equal — is a slashed equals sign "≠" (Unicode 2260).
Most programming languages, limiting themselves to the ASCII character set, use ~=, !=, /=, =/=, or <> to represent their boolean inequality operator.
All of these operators can be found in this table, apart from =/=. I can find this equals-slash-equals used as a way of formatting ≠ in plaintext but not in any programming language.
Has =/= been used as the inequality operator in any programming language?