Do human bodies give off a consistent but unique radiation/electromagnetic/energy signature? Is there any facet of the energy emitted by a human body that is consistent and unique - like a fingerprint, but a signal that could be detected by a remote device?
 A: I'm sure this isn't what you had in mind, but...
Reflected optical light (I can't think of a reason that UV wouldn't be just as good, provided there is enough UV radiation around to be reflected, e.g. sunlight) is 'radiation from a human'. A picture is a pretty good way of identifying humans. Provided the picture is sufficiently detailed (for instance, getting a good image of the iris, or a picture of some fingerprints), this is virtually guaranteed to provide a unique means of identification.
While I'm at it, I may as well quickly go over why other wavelength options you might have in mind are not as practical:


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*Radio/microwave: you could radar a human, but the resolution is roughly limited to the wavelength, so in the radio you'd be seeing at best ~1m scale features, which are roughly similar on all humans. Microwave is a bit better (mm scale), but you don't really gain anything over the optical, and lose some resolution. And I'm sure you can think of reasons that microwaving a human (at certain frequencies) might be a very bad idea.

*Infrared: this is probably the best non-optical option. There is the advantage that humans actually emit (instead of just reflecting) at IR wavelengths, so IR imaging can be used even in the dark. The drawback is that the emission is fairly weak, so it's harder to capture detail in the IR than in a well-lit optical image.

*X-ray: this could be a pretty good option, revealing all sorts of details that an optical image cannot, but humans don't really emit in the X-ray, which means you need a source, which makes imaging "at a distance" much more complicated, at best. There are also long-term health risks to consider.

*$\gamma$-ray: similar problems to X-ray, plus they are more harmful.

A: Indeed, the human body emits biophotons, also known as ultraweak photon emissions (UPE), with a visibility 1,000 times lower than the sensitivity of our naked eye. While not visible to us, these particles of light (or waves, depending on how you are measuring them) are part of the visible electromagnetic spectrum (380-780 nm) and are detectable via sophisticated modern instrumentation.
A: All I can think of is EEG (electroencephalography) signal. It is a diagnostic technique that allows to monitor brain electrical activity by measuring potentials on the scalp. As I know there are some contactless methods of measuring those potentials, but I have no idea if you can measure it from big distance, since it is quite a weak signal.
This is one publication about contactless EEG: http://www.isn.ucsd.edu/pubs/embc09_eeg.pdf
