How to make the value of an input field equal to another field in the same form?

I have a form with two fields at the end, namely:

a) Client Name

b) Client Signature

What I want to happen is the user type in his/her name in the Client Name field and the name gets populated in Client Signature with a different font that would look like its a signature (i.e. Brush Script MT, Rage Italic or similar font)

I have defined Client Signature as Read Only so client won't be able to change or input anything in this field.

Thanks in advance.