One of the problems with Palestine Action is the violent protests they have previously engaged in.

There is a trial in progress at the moment relating to an attack on Elbit Systems where one of the "protestors" seemed to attack a WPC with a sledgehammer. Apparently having caused serious harm to her spine.

https://www.bbc.com/news/articles/c79727zeqyvo

So the folks holding signs expressing their support for the group once it has been proscribed (I believe under the TA 2000) are somewhat ill advised.

If they disagree with the proscription, what they should probably be doing it assisting in the Judicial Review of that proscription which is currently ongoing. Certainly they should be waiting until after the review before expressing any support.

As even if the proscription is overturned, those who expressed support for what is currently viewed as a terrorist org may not have the personal consequences of their support undone.