Lots of sci-fi franchises (Stargate, Eureka, Transformers to name a few) love to throw around the term "energy signature" when they want to indicate that something can be magically identified, measured, located, tracked, or otherwise observed without resorting to technical details. From what I can tell "energy signature" doesn't seem to mean anything in any scientific field but it's near-ubiquitous in fiction. Where did it come from?
Some Googling doesn't reveal any meta-discussion about the term except for a lone blogger comparing it to Applied Phlebotinum (TV Tropes warning). It doesn't seem to be a well-defined trope itself. Outside of sci-fi, most mentions come from the new age pseudoscience realm.
So what's the story? Was it derived from any legitimate science? Is it a running gag among sci fi writers? A backhanded reference to the new age stuff? Do we have an Ur example? (TV Tropes again)