Forwarded emails contain no signature, either above or below the forwarded email body. No means exists in settings to specify that a signature should be in forwarded emails. Thunderbird resists configuration for included signatures specified in the configuration editor.

Account settings > Composition & Addressing > Include signature for forwards

There's no need to use the configuration editor.

Nothing.

Probably the difficulty is that forwards and replies are formatted inconsistently in many ways and the client resists color configuration of reply text for forwards.

• Neither replies nor forwards observe the dark mode configuration for the body of the email being replied to or forwarded. In both, it appears in quasi-light light mode with various elements appearing in red rectangles, instead of dark mode as in the email received. This is a gross rendering failure.

• Furthermore, and quite oddly, forwards and replies inconsistently configure message text. The first failure is that replies are in dark mode and forwards are in light mode. The second failure is that message text in forwards is white, consistent with the dark mode scheme but not with white background, which is inconsistent with the dark mode scheme. The third failure is that the client resists configuration of message text to to any other color. So, perhaps a signature exists in the forwards but becase of this cascade of color configuration failures, is invisible.