Conditional logic and Change to function - can this be done based on a symbol being present vs ==?

I’ve just created a grid cell that I can add numbers, ., and ( ) to. When I click on the cell or hit my enter key after adding a value to it I want it to change to a negative state of the cell if “(” is present.

However, I cannot figure out how to do that with only being able to pick between == and !=.

Does anyone know of a work around? Or, is it best to leave it neutral for now?

What I programmed -

What it’s doing