Disabling a digital signature in LiveCycle

I have a form that have a yes / no question with checkboxes. 

In some cases there should be multiple digital signatures, in others only 1. 

I want the digital signature line to be disabled if the "No" checkbox is selected. 

I would also like the space where the digital singature goes to say "N/A" if the second digital signature is unnecessary.

Is that possible?

Thanks,