Question

how to make a unigue cleanliness poster

Answer 1

IT VERY EASY FIRST THINK ABOUT THE SLOGAN 

than make picture on a paper of children cleaning street which gives the positive view of cleaniness 

than write the organisation name

Answer 2

First give the Heading which no one has ever thought of.You may even take help of internet.
Then write such a slogan by when reading the audience will be forced by themselves to adopt cleanliness.If still nothing strikes your brain then take help of Internet.
Then write ISSUED IN PUBLIC INTEREST and then your group name and address.