Hey Si.........
Out of curiosity..... judging by the bumper in the background, that looks to be about a 2' x 3'. Not too hard to lug around. The OP here, wants to make it 3' x 4' which most people won't be able to handle too well. I'll admit, it can be done, but the abuse the sign will take just hinging two 3' x 4's together... I think it will twist and turn and quickly be unusable, not to mention the scratching and marking up of the edges and legs will take..... unless attached to a frame of some sort will be a useless project.