Caution signs are required to be posted on the door of each laboratory. This way everyone knows what the potential hazards are before entering the room.

Below is an example of each symbol and and explanation of what it means.
 

Room may contain one or more New Jersey Right-to-Know listed materials. Room is used as a primary chemical storage area.
Room may contain materials that are a potential cancer hazard. Room may contain an operative UV source other than ordinary room lighting.
Room may contain radioactive materials. Room may contain an operative laser with a visible beam.
Room may contain recombinant DNA or other transgenic materials regulated at Biosafety Level 1 (BL-1). Room may contain an operative laser with an invisible beam.
Biohazard: Room may contain pathogenic organisms or recombinant DNA regulated at Biosafety Level 2 (BL-2) or higher. Room access is restricted to authorized personnel only.
Room may contain an operative X-Ray generating machine. Inactive Lab: REHS staff post this label on the caution sign when the laboratory discontinues research activities with unsealed radioactive materials and these materials are removed from the lab. REHS conducts a visual assessment and contamination survey of the lab, pending a change in room use or its renovation or demolition.
Radiation Source: This room is designated for use with sealed radioactive sources and generally licensed materials.