If you’re a form author, you will seeing the auto-generated a reference numbers in response table, along with add rows manually or submitted responses. but these reference numbers is unable to copy. you might be copy a reference numbers from excel , and paste them to your specific forms or tables.
I believe that we do not support what you are looking for. Are you looking for a unique reference # for the form itself or for each response from users? Either way we don't really have a corresponding feature.
The form URL for each form is unique but it is not exposed anywhere exept for the URL (IE it is not listed in the My Forms tab of dashboard), I don't imagine that covers your needs.