Hello there :)
I will focus on anti-corruption slogans here. As well as 'call-to-arms' like ones directed at the society as a whole. I hope it will be helpful enough for you!
Don't take it, be fair
[directed at people taking bribes]
There's no such offer, one cannot decline
[one always have chance to say no to a bribe]
Do not turn away, when you see a dirty pay
[nobody should be idle when they see a bribery]
On law you should rely, not a shady aid
[in the long run, corruption makes a country weaker]
You shoudn't have it, if you hadn't earn it
[if you haven't worked honestly, you shouldn't be paid]
No sweat? No GET!
[just like the preceeding one]
Hopefully, it's helpful for you :)
All the best,