[leoedin]

If you have a directional antenna (which would be needed to actually locate the transmitters location anyway) it's actually quite easy to spot GPS signals. It's only because conventional GPS antennas need to receive signals from all directions at once (or at least half of a sphere) that the signal drops below the noise floor. Any signal which can communicate a reasonable amount of data will have to be high powered enough to be easily detected and located by third parties.