I assume I may get a quick answer from the membership on this one, given that there seem to be a fair number on the Board who are lawyers, prosecutors, cops, chemists, biologists, in the medical field or other wise acquainted (ah-hem) with prohibited substances.
Over the last month or to I have run into a couple situations in which a cop has conducted a car search on the strength of the cops assertion that the driver on one of the passengers has a green tongue, and that this is a sovereign, unmistakable indication that the perp. has recently smoked marijuana. Such searches have turned up baggies of green vegetable substance, as the reports phrase it, but it also seems to me that even out here in the sticks any search of a kid’s car has a 50/50 chance of turning up a baggie.
So what is with the green tongue? Is there anything to this or is it just a phony-baloney excuse to rifle the car, call in the dog and generally do a fishing expedition? So far as I know the question has not been presented to any judge around here on a probable cause hearing.
http://www.nps.navy.mil/police/public.safety/119.htm
That was the only place I found it on Google, so it’s apparently not a widespread thing.
Is there such a thing as a Law Enforcement Urban Legend? 
I’m sure there are lots of LEULs out there (like the myth of fingerprints!) This one sounds particularly ridiculous; even if we grant that cannabis CAN turn the tongue green, it’s a hallmark sign of poor oral hygiene, which strikes me as the more common cause (vanadium poisoning can also cause green tongue, or so I’m told). 
Duck Duck Goose, I saw the law enforcement site but it does not give anything more than the conclusion without supporting information. I guess that I am looking for something on physiology and causation. I’m not getting that off the internet or I’m looking in the wrong place. The problem is that cops are using the supposed green tongue phenomena a probable cause factor and, if the search turns up anything, some judges are loath to throw it out on a lack of probable. cause argument. The is a tendency to require the defendant to show lack of probable cause when there should be a burden on the State to show that there is probable cause for the search. Don’t tell me that this is not the way it is supposed to happen, all I know is that it is what does happen.
When I was doing my Pediatrics rotation, it wasn’t surprising to have kids with green (or purple, or blue, etc) tongues depending on what they’d eaten recently. 
Eek! Watch out for that new green ketchup. That turns your tongue green, too.
Right, I’m saying that the fact that there’s not much out there on Google says to me that it’s maybe some kind of Law Enforcement Urban Legend, in other words, not legally applicable (is that the word I want?)