Is it illegal to post incorrect information about someone in public?

I live in a apartment complex and someone posted a note stating that "the people in apartment #xxxx do not clean up after their dog and the smell has become unbearable, go knock on their door and let them know how you feel". This is incorrect Information and is very embarring to us. Is this a form of slander or is it illegal. What can be done about this? I do not know who left it or why. But I wanted to know if it is legally wrong to post my apartment number and ask for people to come to my apartment.