Hi caioDoran :)
Your project sounds interesting and is quite similar to another one I'm working on.
What I can propose you is not creating a C# tool targetting (only) windows mobile, but a more cross-plateform solution based on HTML5.
The idea is to use HTML5 canvas to draw something into it, with a pen or user's finger (for touch device). Then save the content of the canvas as an image (png or jpg).
Advantages of this solution :
- cross plateform : you can target windows mobiles, android device, desktops, laptops if they have a browser installed that supports HTML5 canvas
- having the opportunity to gather few interesting information about the device to enhance your signature feature (like OS type, browser type, device id, etc.)
Problems with this solution :
- the device has to be connected to the internet
- device's browser should HTML5
If my proposal sounds interesting, or if you have questions / thoughts you'd like to share, don't hesitate to contact me :)
Regards,
G.