You missed my point. Read the last paragraph.
Not all employers are upstanding citizens who won't break the law & fire someone for illegal reasons then lie about it. Just because they CAN & sometimes they get away with it doesn't make it legal or even OK.
You can steal a car, too, if you're not caught AND the state has the burden of proof that you actually stole it but that doesn't make it legal.
I don't really have faith in our legal system anymore, I have seen way too many people go free because they had money or talent in sports. From what I have seen rule of law has become who can write the biggest check. Honestly in this case I would carry no matter what the sign says and as long as your the first one there in the morning and you lock up in a safe in your trunk or glovebox and I think you are good to go.