13:16 mark. The mark of the beast, which will be universally required for all transactions, will insure loyalty to the beast, but will also assure an eternal destination in hell for all who accept it (Revelation 14:9-11). This will be some kind of indelible marking, easy to see and impossible to remove.
13:17 number of his name. Maybe there will be three different types of marks, to distinguish three different classes of world citizens.