Using the browser tools you can inspect the signature field as Formidable natively displays it. You'll see that it uses a CSS class "typed". Since that's more than you need, just grab the "font" property from that style, [.font: normal 3em/50px "Journal", Georgia, Times, serif], create your own CSS style with that and use that style in an HTML span element that references the signature field. I just tried it and it works.