That is precisely the reason for the legal banners. It was once common for the login process on UNIX systems to have a phrase similar to "Welcome to System XXXX". That was interpreted in court as tacit permission access the system. There was a mad scramble to update every system in the company to emit the legal prohibition banners in a manner visible before an attempt to login occurs. I had to modify the UNIX systems on 12 UNISYS mainframes in August 1984 to comply with company security. My colleagues with the 3B20S systems had many more systems to update.
Hats off, you've been in industry since before I was born (sixteen months after the referenced date).