I believe, based on the results of this article, that currently the easiest test to see whether your HG2 is real or fake is to ask the following questions:
Look at the color, does it appear as an earthy brown, or does it have a slight purple or reddish tint? A purplish color might indicate a fake.
Is the washer / insulator ring shiny or matte / textured? A shiny washer might indicate a fake.
Is the metal under where the washer would normally lay a dirty brownish color or a more clean steel metallic color? If it is more metallic in color, this might indicate a fake.
Look at the grooves under the top-cap, do they appear small and thin, or slightly larger? Compare them with the photographs in this article. A larger groove and especially a large gap between the positive and negative terminal might indicate a fake.
What markings does your cell have? If it is blank, or is a simple line of text such as 'I0122A', or does it have many markings all over its body? Look at the markings, and see if they match that of an HE2 or HE4. Look at the quality of the markings, are they faded and smeared? If the markings on the steel are faded, it might indicate a fake.