In addition to the 3 kinds of bad aliens, there are certain characteristics to tell them apart in case you run up against any of them.
1. The bad aliens are into crystal-technology. They use it abundantly and it is literally strewn throughout their spacious, oddly-formed space vehicles. In addition to its inherent homeopathic elements, their crystals form two-way transmitters so that they can remain in constant contact with one another. It is not uncommon to spot these bad aliens sometimes chewing on a No. 2 pencil (the graphite lead is but one aberration of their devious technological advances).
2. The good aliens can be seen wearing an abundance of Doc Marten footware, Gap clothes and Abercrombie & Fitch ballcaps. They're only good in the sense that they don't clutter up their nooks and crannies with obscene crystalline structures; they're also considered bad in the sense that they have a propensity for enslaving other worlds through their extensive use of consumerism. They're good only because they can assimilate so well into other species' cultures, seemingly without anyone recognizing them. They tend to have vacuous smiles and dramatic eyebrow movements.
3. The neutral aliens are neutral in the same way that Fox News or Al Jazeera is neutral in its reporting of the migratory flights of birds in the Arctic--truly neutral. They're so neutral, in fact, that their plans for world domination and the complete subsuming of our natural resources is not meant as any affront to humans. Because they are indifferent to our existence--the only time they register us as anything more than large angular globs of matter is when we either sneeze or fart--their only goal is total domination of our world. They do not seek to enslave, cajole or rescue us; indeed, for the most part, they do not even register our sentience.
4. There is a fourth race of aliens, frequently referred to as the B.E.'s, or the Barcode Enforcers. Aside from their constant agenda to imprint unsightly barcodes across people's foreheads or along their wrists, they also operate a legitimate front making actual barcodes for libraries and other institutions that wish to have some form of a record of what's in stock in their collections. Their nefarious ulterior motives can be traced to this business transaction in that they would also like to 'keep track' of humans and their ilk (i.e., pets, mine canaries, plague-carrying rodents). They speak a dialect made up of chitters and squeaks, some thicker (in accent) than others. To them, we are mere wayward souls that need to be accounted for.