From the Ritual of the Calling of an Engineer (Canadian Iron Ring Ritual) part of the obligation is
“I will not henceforth suffer or pass, or be privy to the passing of, Bad Workmanship or Faulty Material in aught that concerns my works before men as an Engineer …”
Your duty is clear, not only should you not seal the drawing but take whatever steps are necessary to prevent this facility from being a danger to the public.
The public is defined here as everyone who may be at risk by entering the facility, whose property is at risk and includes the owners who are asking you to seal something that they may know as substandard.
Failure to take whatever necessary steps to protect the public could and rightfully should result in your PE status being in jeopardy.
I would start by documenting all the deficiencies in the project, including references to which portion of what code are violated and see where that takes you. Document every conversation you have with regarding this issue.
You will want to keep copies of this documentation in a safe place away from the workplace.
If that involves whistle blowing then start blowing. If it costs you your job then start looking for another.
You may not be an employed engineer but you will still be an engineer.
Rick Kitson MBA P.Eng
Construction Project Management
From conception to completion