Is there a symbol for potential equality?
Solution 1:
The most common usage I have seen is
$$a \overset{?}{=} b$$
Usually its context I've seen is before you're trying to prove that they indeed equal or something of that matter.
Solution 2:
≟
The Unicode symbol ≟ can be used for questionable equality.
Unicode Reference: https://www.compart.com/en/unicode/U+225F