We have all seen posters with disclaimers on the wall of an office before. The purpose of these posters is to provide notice to employees about certain rights provided by state or federal law.
The issue of interest for small business owners is: what posters are required by state and federal law?
The Department of Labor has created a website for this very purpose: Department of Labor. (http://www.dol.gov/elaws/posters.htm)
You can answer a series of questions and the site will now generate the list of posters for you with links to download each poster.
While you are conducting this assessment it would be best to also review your current employee review procedures and employee handbook to ensure everything is up-to-date (and to make sure there are procedures and a handbook).