Steganography would be the best choice in this scenario. Steganography is the practice of hiding information within other information, such as embedding a message inside an image or other file format. This would allow the company to embed a sign of ownership within the document without adding any visible or identifiable attributes. It would also make it more difficult for someone to remove or alter the sign of ownership.

XN is a security feature that is designed to prevent certain types of malware from executing in memory. When XN is enabled, the CPU will not execute code that is stored in memory regions that have been marked as XN. This can help to prevent malware from inserting itself into another process's memory location and executing from there.
No-execute (NX) is a similar security feature that is used to prevent certain types of malware from executing in memory. NX works by marking certain memory regions as non-executable, so that the CPU will not execute code from those regions.

Passive scanning is the safest approach for SCADA systems to avoid disrupting their operations.
It detects vulnerabilities by analyzing network traffic without directly interacting with the systems, aligning with CASP+ objective 4.2, which focuses on securing critical systems and reducing risks during vulnerability management.