OSHA requires employers to post a OSHA Job Safety and Health: It's The Law poster in every workplace. It must be placed in a conspicuous place where employees can see it. OSHA recently released a new version of this poster. You can order free printed copies at OSHA's safety poster resource page.
If you have a previous version of this poster, you are not required to get a new one.
OSHA Job Safety and Health Poster Downloads