This should be taken up with the train company.
It could be that the guard is just saying something for convenience sake, in which case he or she needs to be informed to not create problems. That a reservation happens, should be the train company's responsiblity to mark the seat so people know...
Don't be silly - if you want the cow to move, you claim you are palace or millwall, and you just got out for maiming a woman for refusing to serve you alcohol at a supermarket. Then tell her you don't know how to exist on the outside, and you miss your cell-mate.