Anyone with a valid email address can create a free account in the Adobe Sign system.
Free accounts are primarily for signers of documents, and allow any registered email address to view all of the agreements that have been sent to that email box.
Senders that do not attach a PDF copy to the Signed and Filed email may want to make note of the registration URL so they can help their signers gain access to their contracts, without having to send a copy through email.
Signers that want to save their signature in the system may do so once their email is registered.
The Adobe Sign application can only differentiate users by their unique email address.
You as a person may have several email addresses for various reasons, but the application cannot assume different email addresses to be one real person.
For this reason, make sure you are registering only the email address that was used when signing the document.