It consists of a waveform inserted into the non-picture vertical blanking interval (VBI) of an analogue video signal.
There is no blanket legal requirement for devices which record video to detect or act upon the CGMS-A information.
For example, the DMCA "does not require manufacturers of consumer electronics, telecommunications or computing equipment to design their products affirmatively to respond to any particular technological measure.".
Type B signalling (134 bits in total) already defines bits to carry an Active Format Description, Colorimetry, Redistribution Control, and a pixel-accurate definition of the location of any letterbox or pillarbox bars in the image, plus two bytes reserved for future use.
On 50 Hz systems (commonly, though incorrectly known as "PAL"), the bits that are widely used and interpreted as CGMS-A are not named as such, and are added at the end of an existing signalling standard originally created for the PALplus video format (but still in common use in Europe in standard PAL video) called Widescreen signaling.
The 480p signalling is based on the existing 480i standard but with a double speed clock, and IEC-61880-2 formalises this by defining bit meanings which are the same as for 480i.
Hence 480p Type A line 40 CGMMS-A data generated in accordance with CEA-805 cannot signal the aspect ratio of the video image, and in this way is incompatible with the same data generated in accordance with IEC-61880-2, and is no longer a straight "double speed clock" version of the 480i standard.