(14:10-11)Then Judas Iscariot, who was one of the twelve, went to the chief priests in order to betray him to them. When they heard it, they were greatly pleased, and promised to give him money. So he began to look for an opportunity to betray him.
(14:43-45)Immediately, while he was still speaking, Judas, one of the twelve, arrived; and with him there was a crowd with swords and clubs, from the chief priests, the scribes, and the elders. Now the betrayer had given them a sign, saying, “The one I will kiss is the man; arrest him and lead him away under guard.” So when he came, he went up to him at once and said, “Rabbi!” and kissed him.
It is surprising (=unexpected) that there is need of an explicit sign by Judas to make recognize Jesus.
Really did the priests need of a Judas to recognize Jesus ?
Maybe ''Mark'' wants to say something.
Maybe he is accusing some Jewish Christians of having made appeal the first time (before even than Mark) to a invented 'historical' Jesus: Judas who kiss Jesus, calling him a mere ''rabbi'', is allegory of these first Jewish Christians who euhemerized Jesus (to claim authority and power on all the other Christians). Claiming him for themselves.
Therefore ''Mark'' would be accusing ''Judas'' for the same ''sin'' that just him, ''Mark''!, is doing: to betray the true Jesus of Paul, by introducing ''another Jesus''!