Maybe those that don't carry a long gun can carry the signs. It'll be hard to carry a rifle and a sign.
Have to agree here (and was about to make a comment along that line myself before I saw your post). Even with a slung rifle, you really need one hand to keep close control of it. You don't want even a hint of the muzzle sweeping anybody because sure as taxes, somebody would get a picture of it and the headlines would read "gun nut points rifle at...." So one hand to control the rifle, another to hold the sign, then if anything slips or shifts or needs to be adjusted, you're out of hands unless you either let go of the rifle/sling or drop the sign. But then you'd have to pick up the sign and that means bending over (and where is the muzzle pointed then?), or stooping (possibly cracking the muzzle into the pavement) to pick it up. And the video on the 11:00 news "gun nut thinks he's the Keystone Cops."
Long arm or sign, not both. That's my advice.