The very short summary of "how to spot a pump&dump":

Small cap, small volume and an exponential move in price -- that's a pump.

That's when it comes to scams that happen on a smaller scale, but something similar even occurred with a SERIOUS cryptocurrency Etherium (ETH) recently:

A lot of questionable ICOs picked up "investments" in ETH and started selling off their stock when the market projections turned sour. As all of the rats jumped ship almost simultaneously, the ETH price capsized.