I think my point was that the majority of people at these rallies have no idea who the SWP are, and won't think to rip it off or cover it up unless someone tells them. We're living through an age where the politicisation of the 80s and even the 90s ebbed away, and people coming to these rallies are 'fresh' if you like. I mean, there have always been people like that at rallies, but I'd expect there are more now because of the way it's all played out the past couple of decades.
So you have people standing around saying "cover that up" or "rip that off" or you hope people somehow find out who they are on their own.