I think it's a signature in the sense of "email signature", and that the contrast is between a "custom signature" and "required remarks". The required remarks are most likely some branding and legal notices. I guess "accepter" here is more in the sense of "put up with" than "agress to". The custom signatures come before that, and would usually include a standard sign off and a person's name and job-title and some further contact information. Presumably the user has some choice over what these look like.