The poster uses the English word “SELL” to form an isomorphism with the birdcage, which not only implies that the people locked inside have lost their freedom like the birds, but also conveys the idea that they are sold mercilessly.
The black background in the picture suggests the inner helplessness of “people” and their difficult situation in the dark at this time. The use of green for the cage is meant to convey the meaning of “SELL”, since Jamaican coins are mostly green; The use of white not only highlights the picture, but also conveys a hope that you can fly out of the cage and become an independent and free person.