Simply put:
Fear marketing is most effective.
For example, telling people (or making a sign saying):
Put on a face mask to prevent OTHERS from infecting YOU.
The notion of “put on a face mask to prevent yourself from potentially infecting others” is not effective!
Make it cool, sexy, and stylish
Think — if you got all these hipster street wear kids to wear a ‘SUPREME‘ face mask, or a face mask that has fangs on it to look cool.
Or to the fashionista to wear a huge “LV” (Louis Vuitton) face-mask. It must be stylish.