For those of you who are interested in purchasing Gucci dog tags, I wanted to point out a couple of unique characteristics of the ones I purchased from Neiman Marcus that can help you tell the difference between the authentic and the fake:

1) The connector on the chains has a very small double "G" Gucci logo on it, but the fakes are either blank or have a silver hallmark on them.  This logo looks whitish in color.
2) The tags have a clear sticker on each side of them which protects them from being scratched; the fakes are totally clear, but the real ones have a bluish metallic tint to the plastic
3) Don't be fooled by "gift bags", "boxes", etc.  The authentic Gucci tags actually come in a strip of plastic about 4 inches wide with a compartment for the main chain, the small chain, and 1 for each tag.  The chains are sealed in the plastic but the tags are NOT; they are slid in from a slit in the top so you can easily remove them to examine them.  It is up to the retailer to decide how to package the tags at the time of sale.  For instance, Neiman Marcus puts them in a Neiman Marcus drawstring bag inside a Neiman Marcus gift box while an actual Gucci store will put them inside a drawstring bag with the Gucci logo.  The tags seem to always be sold in a velvety drawstring bag.  Many fakes on eBay sell them with a strange polyester bag with the Gucci logo on it that is poorly made (e.g., it has thread trimmings exposed -- not a high quality sewing job at all) -- which almost looks like a strange little sleeping bag.
4) The fake tags on eBay have a legible silver hallmark on the back of the tags or none at all; the real tags have a hallmark so small that it looks like a tiny rectangle stamp at first glance.  You almost need a jeweler's magnifying lens to read it.

Unfortunately, there is a manufacturer who is making genuine silver dog tags the exact shape of the Gucci tags -- completely identical in style.  Other than the hallmark stamp he uses on the back being larger than the Gucci version, you cannot really tell the real from the fake.  I compared my authentic ones to a set a friend got on eBay, and side-by-side, you would never know -- especially at a club where people arent carrying around jewelry magnifiers.