I use multiple custom emails for different entities. On the web based service I have set up specific signatures for each of these entities. However, when I answer an email using my phone app I don't have access to these custom signatures and they go out in a generic style.

I understand that there are users who want the ability to have different signatures on their various devices. That's good too. It's not functional for me but some simple check box that says something like "Use account signatures across all devices" would be great. That way we all get what we need.