Is it illegal to set up a bulletin board for rights protection?

Illegal. According to the query on Zhihu.com, it is illegal to set up bulletin boards to protect rights. It is illegal to protect rights by pulling banners, posting slogans, etc. When the bulletin boards are placed, they have already obtained the approval of the city management department or the village committee or neighborhood committee. If some approval is given, then such a building is actually a legal building, and it is illegal if it is not approved.