The iMore app does not have the signature option. The one created online does not show in the app. It doesn't show to avoid confusion. The app used to have that option I think. TapaTalk does. So what would show if one created a signature online, then created a different signature on the TapaTalk app.? You can use TapaTalk and make the signature the same as what's online.
Sent from CrapaTalk on my ancient but trustworthy iPhone 5.