Can I change the font in one text box to simulate a signature?

You can change the font of a specific field (e.g. a textbox) using CSS. However, I'm not sure I understand how changing the font would emulate a signature field.

If your aim is to allow your users to sign your form before submitting it, you can use one of our signature widgets.

Complete guide: How-to-Add-an-E-Signature-to-Your-Form

In case we misunderstood, kindly get back to us with more info and a better description of what you're trying to achieve so we can better assist you.