A public health campaign rarely changes behaviour through a single clever slogan. The ones that actually shift a habit tend to combine a clear, repeated message with a change to the environment itself, making the desired behaviour the easier default rather than something a person has to consciously choose against convenience every time.
Timing and repetition matter more than most people expect. A message heard once rarely changes anything, but the same idea encountered across a workplace notice, a conversation, a form at the doctor's, and an advertisement over months tends to shift what starts to feel normal, which is usually the real target of the campaign.
The most effective campaigns also make the new behaviour socially visible, so that adopting it starts to feel like joining something rather than standing out. Once a habit is common enough to be unremarkable, the campaign has largely finished its job and the culture carries the rest.