Warnings are very much a part of the legal landscape. While the term tends to take on a one-dimensional definition in the legal world, human factors practitioners tend to consider warnings to be a more general feature of the environment. For example, most legal theories seem to treat written warnings, in the form of placards, stickers, or part of instruction manuals, as the only acceptable embodiment.
In the human factors domain, warnings can be verbal, intrinsically part of the form factor of a product or system, or exist in other forms. Regardless of their embodiment, warnings 
have been well-researched within the human factors community. There are many published studies that relate various features of warnings to their effectiveness, salience, and understandability.
There are cultural factors that affect whether observers understand and heed warnings. Gender can affect the magnitude of risk associated with various types of warnings. Also, of course, there are consensus standards related to the design and content of warnings.
