Hazard signs.

Hazards.
Hazards are something that is very dangerous that can give you the risk of getting hurt or that can cause harm to you or others around you

Types of hazards - 
No.1. - Yellow sign -  hazard -  According to Wikipedia, A hazard is any agent that can cause harm or damage to humans, property, or the environment.

• E.g
• These signs tell you it is dangerous.
• It also means to stay away, so you wont get injured badly.  

No.2. - Blue sign - Mandatory - According to the Internet - This sign means, A "mandatory sign" means a sign prescribing behavior. These signs are required to be blue. A mandatory sign shall show only what action is required. Mandatory signs generally use a white safety symbol on a blue background.

• E.g
• Ear protection - You must wear ear muffs
• Safety helmet, You must wear it to protect your head

No.3 - Red sign -  Prohibitive - According to google, this means, It is a safety sign prohibiting behavior likely to cause a risk to health or safety. These health and safety signs are required red . This sign shall show what or who is forbidden.

• E.g
• Swimming in this area is forbidden