In 2 Thessalonians 3:17, what does Paul say is his mark in every letter?

Answer: His greeting in his own hand

"This greeting is in my own hand—Paul. This is my mark in every letter; it is the way I write."

“This greeting is in my own hand—Paul. This is my mark in every letter; it is the way I write.”— 2 Thessalonians 3:17 (BSB)