Here is a picture of the often quoted "Abbott in front of placards"
I don't think there is any video footage. The questions would be around how did they get there. Were they there and he stood in front on purpose? Did they gather around after he started to speak? Did he give any indication that he knew they were there?
Does anybody really care?
I'm personally disgusted in that large poster. Everybody knows there should be an apostrophe in "Brown's".