Where is the sign?

In the book Mindfulness in Plain English , Chapter 5: The Practice , by Ven. Bhante Gunaratana, he says the following: > As you keep your mind focused on the rims of your nostrils, you > will be able to notice the sign of the development of meditation. You > will feel the pleasant sensation of a sign. Different meditators > experience this differently. It will be like a star, or a round gem, > or a round pearl, or a cotton seed, or a peg made of heartwood, or a > long string, or a wreath of flowers, or a puff of smoke, or a cobweb, > or a film of cloud, or a lotus flower, or the disc of the moon, or the > disc of the sun. Can someone please explain what is meant by this. I’ve been meditating for years and I’ve never experienced such things. Any idea why not? How important is it?