Describing a group of people who lie down in a public place to send a political message

Answered very nicely by Kristina Lopez in a comment:

This looks like a "lie-in" protest demonstration - sometimes also called a "die-in". The protestors lie down in an area, representing dead people, sometimes having signs or banners on their bodies, as your picture appears to show. en.wikipedia.org/wiki/Die-in

From Oxford Dictionaries the following definitions of satyagrahi and satyagraha :

satyagrahi

NOUN

A person who practises the policy of satyagraha: ‘as a satyagrahi, suffering in the path of freedom and justice was part of his creed’

satyagraha
NOUN

[mass noun] A policy of passive political resistance, especially that advocated by Mahatma Gandhi against British rule in India.

• ‘This is where Gandhi developed his concept of satyagraha, translated in the west as passive resistance that, in the end, influenced the whole of the colonial world.’

Origin
Sanskrit, from satya truth + āgraha obstinacy.m