The federal government requires employers, whether law firms or any other type of business, to post certain information notifying employees of their legal rights. There are plenty of companies that will sell you fancy versions of these mandatory posters, but you can get many of them free from the Department of Labor at their Office of Small Business Programs Web page. Here is some information from that page:
Some of the statutes and regulations enforced by agencies within the Department of Labor require that posters or notices be posted in the workplace. The Department provides electronic copies of the required posters and some of the posters are available in languages other than English.
Please note that posting requirements vary by statute; that is, not all employers are covered by each of the Department’s statutes and thus may not be required to post a specific notice. For example, some small businesses may not be covered by the Family and Medical Leave Act and thus would not be subject to the Act’s posting requirements. For information on coverage, visit the Employment Laws Assistance for Workers and Small Business (elaws) Poster Advisor. You may also contact the Office of Small Business Programs, for assistance with these notice requirements.
To obtain posters or for more information about poster requirements or other compliance assistance matters, you may contact the U.S. Department of Labor by telephone at 1-888-9-SBREFA, or by email at Contact-OSBP@dol.gov.