...drill & plug a few holes and use 4mm screws and penny washers... a few easily filled holes won't look as messy as strips of bare concrete..
When your banner is wrapped around the windscreen of the school bus don't expect to hear anything from 3m save the sound of footsteps receeding into the far distance at great speed.
Doug's idea of using a rigid board sounds more likely to work... all it takes is for a puff of wind to get behind your banner and it'll be flying off down the road.
If you have to use banner drill & plug a few holes and use 4mm screws and penny washers... a few easily filled holes won't look as messy as strips of bare concrete which you'll undoubtedly get when you rip the tape off the wall.