Its published or people work it out. If you look at the reviews on dpreview, you'll see that they list things like actual number of pixels on the sensor, effective number of pixels on the sensor, arrangement of colours in the filter and a whole bunch of other information.

As for whether you can spot the difference yourself just by looking at the output then no idea.

SuperCCD is advertised as a unique feature of Fuji cameras since as Tony previously said, it alledgely gives you a higher effective resolution than the actual number of physical sensors in the CCD.

As for other cameras, any deviation from the regular image sensor is generally noted in the specifications. Canon use a different set of colour filters which again apparently give better results than the regular colours. Sony use another arrangement etc...