Proscription means it is an offence to belong to the organisation, invite or recklessly express support for them, arrange a meeting in their support, or wear clothing or carry articles which arouse reasonable suspicion that you are a member or supporter of the organisation.

So under the law, waving a Palestinian flag is fine. Waving a Palestine Action banner is illegal.

This amounts to a targeted action at the organisers and perpetrators of the incident, rather than wider supporters of Palestine.