I don't have an opinion on what the mark is. All I know is what the Bible says. For all I know, it will involve a mark/credential, a name and/or a number. 

In Revelation 13:16 we will see that the beast (the second beast that is introduced in Revelation 13:11) causes all to give (Greek didomi, Strong’s Concordance reference G1325) a mark (credential).

 If you are caused to give a mark, name or number of a beast in order to buy or sell -- then the mark is here.

A BEAST is a government.  A Beast issues a mark. 

Revelation 13 predicts that a two-horned beast issues the Mark. Nowhere in Revelation 13 is there a one-man world leader. If you want to insist that a one man world leader issues the mark, then you must first explain away three angels' messages:

1. Angels insist that horns symbolize kings while beasts symbolize governments. Angels (in Daniel 7:24, Daniel 8:20 and in Revelation 17:12) tell us that the horns symbolize kings that came out of the beast kingdom, perhaps successive kings. Or perhaps concurrent kings. (Or perhaps, as implied by Isaiah 33:22, kings refer only to the executive branch of government).

2. An angel, in Daniel 7:23 equates Daniel's fourth beast with a fourth (final) world government, not a church, not a man, not an antichrist. The word "antichrist" is not even in the book of Revelation.

[although I don’t have proof, I highly suspect that the United States military has something to do with Daniel 7’s fourth exceedingly dreadful (Daniel 7:19) iron beast that assimilates and takes away the dominion of other beast powers (Daniel 7:12), consume and trample down the whole earth and break it to pieces (verse 23).]

3. The two-horned beast causes all to worship the seven headed ten-horned beast. Unless these angels lied, all you can conclude is that the final world government is two loosely knit confederations of worldly powers totaling 8 heads.