I was not clear about what is a danger sign, what is a warning sign and what is a caution sign, till I read this article in Safety Daily Advisor. It also explains about biological hazard sign and instructions.
Danger sign is about a hazard that can lead to death, warning sign is about potential hazard and caution sign is in-between.
Whatever be the display of signs, the articles mentions, that if one can't understand what it means and what should be done, then it serves no purpose.
It's better to provide training and provide booklets containing the information to all employees. Also, display the measures to be taken, near the area where it can be seen by the employees.