The message is a general one the Moneydance developer has included for any Extension that he has not signed.
Complaints have been made about this especially by people who want to write and use their own extensions and have no desire to make them public or submit them for approval.
The Moneydance developer has indicated he intends to tone down the message somewhat as he does not want to discourage developers.
The developer of the Quote Loader has said he will work on the extension to make it able to be signed. This will not be an overnight task, it cannot be signed in its current form and the changes are not trivial.