What is the Seal God places on the foreheads of the 144,000 in Revelation 7? Sealed by the Holy Spirit or the word Emet (Truth)?

I am trying to determine exactly what the Seal placed on the 144,000 by God was. I have heard two directions and I want to see what everyone else might say. The word Truth or Emet would be in John’s style, but others assume the Holy Spirit…