Hi there David!
Don here from Shopify!
Thanks for taking the time to post here outlining your requirements.
As you've seen, there currently is no functionality in the mobile app to collect a signature as you need.
I've spent some time looking into this and working with some other teams here to see if there are any possible workarounds.
This is less-than-ideal obviously, as it sounds like you were hoping to collect your customers' signatures digitally?
It is actually possible to collect signatures digitally when using the POS app, though this would only work where the order is being paid via POS and not online.
What we can do for you from here though is to file a feature request with our developer team so we can see about getting this added in a future build of the platform or apps.
Let us know as much as you can here about what you'd like to be able to do so we can file the best request possible here.
Thanks again for letting us know about this!