I don't see the word "NOT"

Old Mr Blank loved shooting bears, but his eyes were not good any more. Several times he nearly shot people instead of bears, so his friends were always very careful when they went out shooting with him.

One day a young friend of his wanted to have a joke, so he got a big piece of white paper and wrote 0n it in very big letters: "I AM NOT A BEAR". Then he tied it to his back and went off. His friends saw it laughed a lot.

But it did not save him. After a few minutes Mr Black shot at him and knocked his hat off.

The young man was FRightened ans angry, "Didn't you see this piece of paper?" she shouted to Mr Blank

"Yes, I did," said Mr Blank. Then he went nearer looked carefully at the paper and said, "Oh, I am very sorry. I didn't see the work NOT."