Does it mean the employee is resigned or does it mean he got fired?
I'm guessing this is internally sent. The memo is meant to tell you not to forward anything to him and if seen on company property raise suspicion. It could be he was previously in charge of many things or customers, and if that's the case, the message would make sense that you could tell ...
However, the experienced employee also prefers not to move to the second office that has come available.
He has indicated his preference. Inform him that it will mean sharing so he has a chance to change his mind, then go ahead. He can't complain if it's his idea. Some people prefer to share.
You mentioned that this is making you anxious, so let's approach this from that side.
It is fairly normal behavior to turn out lights, even in other people's rooms.
As others have mentioned, this could just be someone overly environmentally conscious or someone trying to save the company money.
I have had both sorts of coworkers.
An example of one is a ...
In a comment, you clarified your goals:
I think my goal is to keep lights on in my office. And as a greater goal, have people generally stay out of my office unless they have a business with me, or they are HR, or perhaps my boss or someone directed by them
Given your first goal, it seems like there are many things you could try:
Shut and lock your door ...
It is not related to saving electricity because if it was, there'd be a company-wide message, and someone would come and address me directly.
It is not related to a formal corporate electricity-saving initiative. It could easily just be someone with an interest in saving electricity.
And it may not have been intentional or part of a plot. My father ...
What do I do?
I would do nothing but turn the light back on.
Most likely it is someone who is eager to save the company money regarding the cost of electricity or they are attempting to do their part for the environment.
In either case, it takes no time to just turn the light switch back to the on position. Don't let this little thing mess with your ...