The design is deliberate in allowing quick recognition of the information being communicated, in order to increase efficiency and clarity.
The theory behind visual control is that if something is clearly visible or in plain sight, it is easy to remember and keep at the forefront of the mind.
Another simple example of a common visual control is to have reminders posted on cubicle walls so that they remain in plain sight.
Visual signs and signals communicate information that is needed to make effective decisions.
These decisions may be safety oriented or they may give reminders as to what steps should be taken to resolve a problem.