Why not print several and hand them around to those without a placard? Most people will appreciate the offer and then think about the message too. Home printing or hand painting are all options that would work, or splash out at the local print shop.
Good to know, when you type #AusCarbonDividend into a search engine it goes to this informative University of New South Wales website here. Here is a handy link to some of the kid's own posters.