Careful reading of the specific location of the genset, and WHY it is being installed has to be considered.
Article 700, 701 & 702 have to be reviewed, with 700 and 701 being the most stringent, as one is for Emergency systems, and 701 is for Legally Required Systems. 702 is commonly used for gensets at comm and industrial facilities for 'backup power'. Often, it is inadvertantly called "Emergency", but does not meet the requirements of 700.
The 'marking' for Optional are 702.7 (a)&(b).
A typical 'large' 702 genset may have two panels with chosen circuits, panels being marked 'Generator Panel'; 'Critical Circuit Panel', etc.
What things are labeled or called may or may not be what they are within the NEC definitions or intent.
700.2 from 2011 NEC:
Emergency Systems. Those systems legally required and
classed as emergency by municipal, state, federal, or other
codes, or by any governmental agency having jurisdiction.
These systems are intended to automatically supply illumination,
power, or both, to designated areas and equipment
in the event of failure of the normal supply or in the event
of accident to elements of a system intended to supply,
distribute, and control power and illumination essential for
safety to human life.