I think "f(x) = 7" is always equality of the evaluations, and if you want equality of the functions you should write "forall x, f(x) = 7". Admittedly mathematicians are lazy and don't always write that when it's clear from contex, but I don't think the ambiguity is caused by the "=" sign. The expression "f(x) < 7" would be equally (ha) ambiguous.