Many people who wish to ridicule Jehovah's Witnesses often resort to asking the same old, childish question: "What Have Jehovah's Witnesses Witnessed?"
However, this question may prompt some to consider a legitimate and somewhat related question, "How Did Jehovah's Witnesses Get Their Name?"
The key here is to understand exactly what "witness" means in this context.
According to the Theological Dictionary of the New Testament, "the concept of witness [is used] both in the sense of witness to ascertainable facts and also in that of witness to truths, i.e., the making known and confessing of convictions." So a witness relates facts from direct personal knowledge, or he proclaims views or truths of which he is convinced.
So a "Witness" is someone that speaks publically about what he knows to be true. Of course no human has ever literally seen God (John 1:18), but Jehovah's Witnesses realize that God has asked his faithful servants to be His Witnesses and to tell others about Him:
"Ye are my witnesses, saith Jehovah, and my servant whom I have chosen;" (Isa. 43:10) - ASV
Isa. 43:10 also corresponds with Acts 15:14 where it says that God will turn "his attention to the nations to take out of them a people for his name." (NWT)
According to the Bible, the line of Witnesses of Jehovah reaches back to faithful Abel. Hebrews 11:4-12:1 mentions this line as a "great a cloud of WITNESSES surrounding us."
The Bible says that Jesus Christ was the foremost witness of Jehovah: "These are the things that the Amen says, the faithful and true witness, the beginning of the creation by God." (Rev. 3:14) Considering the definition of "witness" mentioned above, Jesus said that it was his Father's name that he made manifest. (John 17:6)
For more, see:
How We Came to Be Known as Jehovah’s Witnesses (Pastor Russell)