Manage them what kind and how? I know you think everyone wants to do whatever it is you are wanting to do and the answer should be simple. The rest of us have no idea because you have not actually specified what you are wanting to do.

Have you read the support article? https://support.mozilla.org/en-US/kb/signatures Do you mean something like this addon offers https://addons.thunderbird.net/en-US/thunderbird/addon/signature-switch/?src=search

You might even be asking about s/MIME signatures although that is a less mainstream thing than a general email signature.

Matt, sorry for the lack of specificity.

I set up signatures in TBird and want to know how to manage them so they show up in new emails and also in replies to responses. That's not happening. I hope this clarifies things.