The billboard says "Watch your language".

"Watch your language" on the billboard means that the place or activity requires people to communicate and communicate in Mandarin. This is a measure to promote national language unification and cultural exchange. Mandarin, also known as standard Chinese, is the official language of People's Republic of China (PRC), and it is also widely used in education, government, media and business. By encouraging the use of Putonghua, mutual understanding and communication between people can be enhanced, and social integration and development can be promoted.

Advocating the use of Putonghua will not only help to strengthen the national language unity, but also reduce the communication barriers caused by dialect communication. In addition, encouraging the use of Putonghua can also promote cultural exchanges and blending in different regions and enhance national unity and social harmony.