Thank you for your post.
At this time, the Signature Capture will only display "Sign Here".
I recommend that you enter this "Draw Here" (or whatever you want displayed) suggestion into our Feature Requests web form at:
These web entries are monitored and read by our Development and Product Management departments where they are discussed and considered for future releases. Although I could copy your post and paste it into the web form, there are a couple of questions asked that only you can answer.
GoDraw has this feature.
It uses the web viewer. It captures your drawing into a container as url base64.
I played with the demo, but I would like to make a custom skin. You have four theme options.