work with an art school in the area. Have someone sketch out the outline and people paint it, yeah, for the honor of doing it.
We have a mural wall here that gets a panel done every summer. the head artist sketches it out and then will have people volunteer to paint. I do know that she sometimes has to go behind them and ‘fix’ things, however that’s a mural of scenery and people, these signs are likely more simple.
If people are providing the talent, then they will ‘own’ the art/signs, and it’s less ‘kids pranking ‘the man’ by stealing them’ and more ‘thugs abusing the hard work of talented artists’
There’s no rule saying that signs can’t be artistic and creative…they just have to be readable and understandable.