Compilation of all so far:
Not: Szeth, Dalinar, Elhokar, Vasher, Shallan, any Herald, Silence Montane, or Zo. Hints:
The first two things are more mundane than they seem.
It is not the light that brings fear, but the truth it reveals. And the pact was only half fulfilled.
The pact is more important than what marks it.
The blood is quite literal. The second thing is just black ink, the half fufilled pact is more important. Actually, all four things are more mundane than you think.
The speaker is from Roshar.
This boast was meant to be misleading, so look be careful with people who seem to fit very well without some alternative interpretation.