Hm, this has always worked fine for me. Sorry for asking the obvious here…
Are you sure that the ticket has been assigned to the group? Try to discard any open changes to the ticket, assign the correct group, click update, then try “reply” again. Changing the group without clicking on “Update” while replying does not work.
Are you sure that you’re replying via email? As far as I know, signatures work only for email replies. So do not click in the “Enter Answer or select attachment…” field below the customer article, but on the small “reply” button beneath the customer article instead.
Though by now I’m beginning to think that this might count as a bug; at least it’s inconsistent:
When you create a new ticket, Zammad will automatically update your reply with the correct signature whenever you change the group. No need to discard the half-written answer, just make sure you’ve chosen the correct one before hitting Create: