Slogan:
A short and striking or memorable phrase used in advertising.
(As often used as a campaign.)
Population Control:
The practice of artificially maintaining the size of any population.
(Refers to stabilize the population of certain areas/municipalities)
Therefore,
You'd have to create a slogan about population control used as a campaign.
E.g:
“We Control The Growth Of Every Other Species, Except Our Own.”
“More people=less open space.”
“Use a lid have just one kid.”
