I told you so
another reason for the company to send the memo out is perhaps not to stifle any current ongoing issue, but to serve as a placemark for what their rules are. Then if an employee breaks the rules they can't claim ignorance of the rules and hence unfair dismissal etc. So it's like the safety signs plastered everywhere these days, tannoys in DIY sheds saying keep your children next to you etc etc, if the company can reasonably prove they told you so, then they're not liable for whatever catrastrophe unfolds.
In the old days it was called common sense, but now there appears to be zero value placed against having any!
G