Thank you for your message.
In this case its best to require registration to fill forms. You can achieve this rather easily. If you open the Form webpart you can see the **Visibility ** section. What you can do is choose to display it only to authenticated roles. Now user needs to be logged in order to even see the webpart.
Other then this you can have another webpart, such as editable text, and this one will be shown only to non-authenticated users saying that they need to sign in to submit forms.