I had the same impulse, and then it struck me: maybe, just maybe, trying to replicate my hand-written signature on an unknown website that's obviously doing it's best to capture hand-writing is not the absolute best strategy, security-wise.
Not saying the author of that pad is evil or anything, I just questioned my own impulse. And stopped drawing. :)
John Hancocks arent particularly secure anyway, and I actually have little use for my digital version, other than using it on documents to be sent to people. Everything else is handled via other ways (or require actual pen on paper!) :)