In short, I don't have ANY information on the mark of the beast. Ha ha. I haven't a clue what it is, when it'll come, or what it will entail. I have, however, heard of some of the more popular theories regarding the mark. Some entertaining theories include:
The "peace" symbol, the number "666" (which is actually indicative of Nero), microchips, cell phones, bar codes, this thingie, and the world wide web. I have no doubt this is a very short list considering the joy folks seem to get out of picking apart these theories. To my friend, however, I say "Don't worry about it." All one can do is pray for discernment when and if the time comes. This mark may not even appear for another 600 years! Maybe it's already here. Who knows? I certainly don't. And I'm not typically one to go on any wild goose chases to find out.
But hey - I guess these theories are interesting enough to warrant a random chat. But to fear them? No. It is better to simply place those worries at the Feet of the Lord and pray that if we are meant to bear the trial of the mark, we are given the wisdom, clarity and strength to bear it in accordance with God's Will.