Signature capture is a really important for LOB user applications. I have tried using a canvas component in a HTML panel to implement signature capture but performance is poor, freely available apps on Google play such as SIGNificant work much better. Do you have any plans to construct a signature capture control?
Signature Capture
As you use HTML5/JavaScript to create the app in Appery.io, to add signature capture would need to be done via Canvas API.