I'm not sure there are any specific idioms -- I think you might be wanting slogans or mottos instead.
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litter
were bitter about litter
No slogans in chemistry !
horsey (in high pitched voice)
mile high city!
litter
were bitter about litter
Do not litter!! Use bins!
Fnevvy
Cleanliness is health
Class of Swag16!
"Do it again in 2010."
ritans paradise
No slogans in chemistry !
say what you think
horsey (in high pitched voice)
mad river is mad