Ok, so far we have the following options:
= // assignment
== // check
:= // or..
int x = .. // assignment
== // check
3)= // both assignment and equality check
I personally prefer #1, as it is the most C-like. (And indeed does not require pressing additional keys)
I am not a huge fan of #3 because it would have to be excluded from expressions where its hard to tell whether its an assignment or a logical operation:
bool isPressed = (reading = 3) // or
bool isPressed = isOn = 1 // etc.