It's Unhygienic
Maintaining cleanliness and hygiene in public restrooms should be a standard practice. When a sign like this is necessary, it raises concerns about the extent of the issue it aims to address. In this case, the sign explicitly instructs patrons not to urinate in the sink.
The presence of such a sign suggests that the restroom's cleanliness had been compromised, emphasizing the importance of responsible and hygienic behavior in shared spaces.