A suggestion for the section on signatures in the useful Help page.
How Do I Set Up A Signature For My Account?
To set a signature for your account, go to the Subscription page for your group (it's the 'Subscription' tab in the left hand sidebar when viewing your group). On the subscription page, look for the 'Use Signature For Web Posting' checkbox and check that. Then you will be able to add a signature. Once complete, click the Save button at the bottom of the page to save your changes.
I suggest that you change “account” in “to set a signature for your account” to “to set a signature for a group”.
And add that each group you subscribe to (or each subscription) can have a different signature. Or “the signature is for a specific subscribed group and you can set a different signature for each, if you wish."
It works, just tested that.