The taste of a pill is the best indication as to its content. MDMA has a characteristically very bitter taste. Scratch off a piece of the pill and put it on the tip of your tongue. If it doesn't make your face wince it probably doesn't have much good to it. Typically, the worse it tastes, the better it is. E-pills also have a characteristic "sassafras" smell, because of the use of sassafrole in the synthesis of MDMA.

Be sure to pay close attention to the appearance of the pill, namely its color, the stamp, thickness, how hard it is, whether there is a score down the back, whether there are speckles, and other stuff like that. If it looks like crap (ie; crumbly, no stamp, etc.), it usually is. Obviously, the more E pills you see, the easier it will become to distinguish between copycats.

It is always a good idea to know what you're getting. The best way to discover what is in your E-pill is to purchase an E test kit. More info can be found at The EZ-Test Page.