John is barefoot and wearing simple clothes but seems to be missing his leather belt –
“Now John wore a garment of camel’s hair and a leather belt around his waist …” [Matthew 3:4].

The banner attached to John’s staff reads “ECCE AGNUS DEI !” (“Behold the lamb of God”, in Latin) –
“John was baptising people in the river Jordan when he saw Jesus and cried out, ‘Behold the Lamb of God who takes away the sin of the world!'” [John 1:29].

The scallop shell at John’s left hip is a common symbol for baptism. It was and still is used in many places for pouring water over the head of the baptised person. It’s unlikely that John did this as he practiced total immersion. In his case, the shell is simply a reminder that he was the Baptist or Baptiser.

John has his hand and forefinger raised, ready to give out to the Pharises (and to us?) –
“But when he saw many of the Pharisees and Sadducees coming for baptism, he said to them, ‘You brood of vipers! Who warned you to flee from the wrath to come?'” [Matthew 3:7].

The JB monogram at the bottom of the window tells us that this is indeed John the Baptist, in case we hadn’t already guessed from the other clues.