Legal Question in Construction Law in California

If you are referring to highway signs, at construction zones or in general, I think this is covered in one or more AASHTO Standards Manuals (American Association of State Highway and Transportation Officials), which are adopted in most states and which could be discussed with judges or juries as recommended practice, if not mandatory.

If you are talking about construction zones in general, warnings should be designed, worded and placed so as to give notice to the public, including short people, children, people in wheelchairs, whomever is foreseeable, of known hazards. There might be some standards put out by some trade organization, but as far as laws requiring this-or-that, including height, the size, shape, configuration, etc. of construction signs, I think there is too much variation from site to site for the legislature to have specified a particular height or range of heights.

For highway construction in California, I believe the CalTrans Standard Specifications govern signage requirements for the contractors to follow, as well as barriers, flag personnel, etc.