Compare the look of your shoes with the description and pictures of the same version on Nike.com. Nike's website maintains a vast catalog featuring photos of every shoe series they have ever released, including the Vapors. These pictures are high quality, allowing you to see the fine detail that is supposed to be on the shoe. If your Vapors have any comparable differences when when contrasted with the pictures of the genuine article, they're likely fakes.
Go through the "Fake Nike Shoes Guide" at StreetSense.com. The Fake Nike Shoes Guide provides images of fake shoes and compares them to the authentic versions, allowing you to consider and learn the differences between the two. The guide also points out what brands (including the Vapors) are often counterfeited.
Look at the stock keeping unit number on the box that the Nike Vapors came in. Compare them to the stock keeping unit number printed on the identification label on the inside of the shoe itself. If these two numbers do not match, you are likely looking at a fake pair of Nike Vapors. Every pair of Nike shoes, including the Vapors, has their own unique identification number designed for these purposes.
Examine the Nike logo present on the tongue and side of the Nike Vapors. The Nike Vapors feature a raised Nike logo. If the logo on the shoes in your possession is flat or looks like it was stitched with regular yarn or similar material, the Nike Vapors are definitely fake.