So I wrote this book Supernice about an alien invasion. The aliens create a dystopia of oppressive new rules and terrible consequences for breaking them. In response, the government replace advertising hoardings with posters that politely (and then not so politely) tell the public how to behave to avoid trouble. Following are some quotes from the book. (And the book can be acquired for a dollar, to your right, if you fancy)

At first the messages seemed friendly:
Advertising hoardings stretched along the seafront. Usually they were filled with adverts for phones or cars, but now the adverts were in pastel shades of purple and pink, with butterflies and smiling faces. In large letters the messages were simple:
SHOW LOVE, NOT HATE
PSST, YOU’RE BEAUTIFUL, PASS IT ON
But even then, Natasha was suspicious and happy to see signs of rebellion:
As she headed back home, Natasha passed a hundred more pink posters in bus stops and stuck to lampposts. Some had already been defaced.
KINDNESS SPREADS was graffitied with DESTROY!
And LOVE UNITES US in purple, with FUK DA ALIENS in angular black writing over the top. Natasha had never liked graffiti – she always thought it made a place look messy – but this was righteous.
And finally as the oppression became more extreme and the pretense ended:
The main road had changed again. Instead of advertising hoardings with hippy messages, now there were screens, each showing an order.
POLITENESS IS NECESSITY and SHOW RESPECT and DON’T BECOME ONE OF THE TAKEN.
I wanted to create an atmosphere of tension and uncertainty, but one in which people needed to find a way to not only survive, but to still laugh, still connect, still keep going. And of course they wanted to dupe the aliens and escape too.
Well now I’m back at work, I’ve discovered that is exactly what London has become. Lots of instructions with cute pictures, saying Cover your face, Keep your distance, Don’t travel unless you have to. It’s all considerate messages for our own safety, but the atmosphere is still intense. With half our faces covered, people are more suspicious of each other, and anyone could be a virus carrier. But we still need to laugh, connect and keep going. Luckily we don’t need to worry about the alien bit. Yet.