One of these people may be breaking the law (soon). The gentleman on the Right is playing "King James I" and is entirely safe. The gentleman on the Left is playing "Guy Fawkes" and could be at the risk of being guilty of glorifying terrorism.
In the same way any boys who ask for "penny for the guy" next year are taking a risk (particularly if they use a sign).
To be fair anyone could be locked up for 28 days whether or not they display a "penny for the guy" sign.
The Violette Szabo museum is also taking a risk as is anyone playing a videotape of "allo allo".
I accept entirely that the Attorney General may decide that prosecuting such people is not in the public interest, but before I dress up in a Guy Fawkes costume I would wish to get an agreement from the CPS not to prosecute.