Hi there,
Is this a bit what you’re looking for?
Preview:
Edit page:
https://bubble.io/page?type=page&name=data_image_png_base64_ivb&version=test&id=lenex-test-environment&tab=tabs-1
When you insert a signature, it will call upon the POST API that I created using Javascript, which will enter the string that the HTML outputs into the database. This might still not be idea, but it might be the ‘edge’ or ‘idea’ you need to move on? 
Regards,
Olrik