What exactly is the text of the warning you are seeing?
If it concerns authorising a certificate (which sounds likely from what you’ve said), this is nothing to do with your personal identity. It is likely to be the Chrome browser (not diaspora*) noting a discrepancy in the authentication certificate provided by sysad.org that’s used to verify an HTTPS connection.
It is probably the Chrome browser asking if you are willing to trust that remote site and therefore to receive content from that domain in your joindiaspora.com stream in spite of the problem with its certificate of validity. This would not touch on your anonymity or personal security at all. The only security it would touch on would be your computer’s security from being infected with malware.
This usually happens because a security certificate has either expired or has become corrupted in some way, both of which would produce an alert from a security-aware browser.
sysad.org is a long-standing pod and can be trusted, if you want to see content from it in your stream. Otherwise you can continue to refuse the authentification, or you can ignore any accounts from sysad that are appearing in your stream, which would stop that content from being provided and therefore stop the warnings.
This is all assuming that the warning relates to an HTTPS security certificate. If you paste the text of the warning here (removing any personal details that might be included), we’ll be able to give more specific advice.