During the Cultural Revolution, customers had to treat shop staff with respect and submission: the workers were the bosses. Now kindness and politeness from the staff towards customers are encouraged again. The text on the wall in the background describes the desired attitude: "Active, enthusiastic, patient and thoughtful" (主动热情耐心周到 - Zhudong reqing naixin zhoudao).
This poster actually was designed and published in 1965. But it soon became obsolete - or even counterrevolutionary. Apparently the design was judged good enough to be reprinted after so many years, and to get a second chance under new political circumstances.