What does the fourth sticker in Xi'an mean during the epidemic?

Representatives have completed four rounds of nucleic acid collection.

Recently, when Xi'an carries out large-scale nucleic acid screening in the city, a cartoon sticker will be issued to citizens as a voucher for completion of sampling.

Xi'an will issue a "Four Treasures of the Qinling Mountains" sticker every time it carries out a city-wide large-scale nucleic acid screening. From the giant panda to the golden monkey, to the takin, and then to the Zhu_, Xi'an people's "friends" "Circle" was flooded with the "Four Treasures" stickers that appeared collectively.