MUTCD General Guidance
... engineering judgment is essential to the proper use of signs, the same as with other traffic control devices
Information of a less important nature and extraneous information should be moved to less critical locations or deleted
A conservative use of regulatory and warning signs is recommended as these signs, if used to excess, tend to lose their effectiveness
In situations where messages are required other than those herein provided for, the signs shall be the same shape and color as standard signs of the same functional type