I put the approval signature item over my seal - so it shows the date/time I sealed it. I also include data such as the client and the project in my digital authorization.
Bluebeam won't let you edit a PDF with a password protected seal authorization on it, and when you print to PDF, it will remove my digital signature. Without the digital signature, the drawings aren't supposed to be used for construction. Could you have unscrupulous contractors, yes, but that's what contracts and client vetting are for.