I quite like the way the language is really specific here, as it brings out that nice "jobsworth" official Tube tone "If you fail to hide your true emotions fully or make any attempt to engage with passengers".
I've put in bold where I imagine the emphasis would be if this was ever to become an announcement.
My blog posts will be a bit sporadic over the next two weeks, as I'll be in California for work. I'll be thinking of you & hope your commute & travels aren't too problematic. Whatever you do, make sure you follow the signs about your emotions to avoid the penalty fare.