Make sure docs are up to date for Signature usage

[chriskrycho]

I did a pass a while back which caught some of this, but as this discussion on Discourse indicates, we have at least one spot (and, more likely, a number of spots) in need of updating to match how we model the world with Signature in view, including specifically how to refer to the Args type in a constructor.

[roomman]

Aa promised, added a PR for this: #1530. 👍🏻