Ironic, since one of the reasons I’ve heard posited AGAINST E-Cigs is that people could be smoking pot with them and nobody would be the wiser. Can’t have that now, can we?
Since the e-cigarette produces water vapor which dissipates (versus smoke, which does not so much), and the e-cigarette has little to no smell, one would have to be pretty clueless to not be able to tell the difference.