R20:33.

He will not sign or seal plans or specifications prepared by someone other than himself or an employee under his supervision.

[See Code II.2.b. ]

Code is relevant when:

Engineer signs or seals plans or specifications

Code is violated when:

The plans or specifications were not prepared by the Engineer
AND
The plans or specifications were not prepared by an employee under the supervision of the Engineer

Code is not violated when:

The plans or specifications were prepared by the Engineer
OR
The plans or specifications were prepared by an employee under the supervision of the Engineer