Rev. 19:16 “And He has on His robe and on His thigh a name written: KING OF KINGS AND LORD OF LORDS.” This is the same name stated previously in Rev.17:14 and 1Tim. 6:15; qualifying him as the only Potentate.

Revelation 19:16 His name written on His vesture and thigh' was partly on the vesture, partly on the thigh itself, where, in an equestrian figure, the robe drops. (from Jamieson, Fausset, and Brown Commentary)

Revelation 19:16 On His thigh. Some explain, on the garment where it covers the thigh to which the sword is bound. Compare Psalms 45:3. Others, partly on the vesture, partly on the thigh itself, where, in an equestrian figure, the robe drops from the thigh. According to the former explanation kai (NT:2498) "and" is to be taken as explanatory or definitive of the words "on His vesture." Others again suppose a sword on the hilt of which the name is inscribed. Expositors refer to the custom of engraving the artist's name on the thigh of a statue. (from Vincent's Word Studies of the New Testament)

Revelation 19:11-21 The ensigns of his authority, his coat of arms-a name written on his vesture and thigh, King of kings, and Lord of lords, asserting his authority and power, and the cause of the quarrel, v. 16.

(from Matthew Henry's Commentary on the Whole Bible)

Revelation 19:16: "There are several such images yet extant, with an inscription written either on the garment, or on one of the thighs, or on that part of the garment which was over the thigh; and probably this is the meaning of the apostle” (from Adam Clarke's Commentary)

Why does this make sense, because it will be seen by people. The Greek word is epi, i.e. over, upon,

it means upon, not in, as an engraving Gr. en, not in the skin.

I believe the meaning is that this inscription is written on his robe in the area of his thigh, not a tattoo on the skin. It is on the garment where it covers the thigh, otherwise his robe would be quite short and not like the robes they wore, nor that a high Priest would wear. As there robes often went to the ankles.