Hi @electricity, welcome to our Community!
As a Dropbox Sign user, you should be able to control your Notifications by hovering your mouse over the email in the upper right of any page in your account and then selecting Settings.
Or you can use this link directly. If you scroll down to the second section of the page you will see the Notifications area there, and there is one that says: When someone signs a document I sent.
Can you give this one a go?
Keep me posted!