How can I know that I am clear of thoughts while I am meditating?

While meditating, one might try to be aware of their surroundings, to be present in the moment. But how can we become aware of it without *thinking* that we are aware? Another example is when one can *listen* to sounds or silence, and even if one is not trying to put *stories* behind the sounds, one might find oneself *thinking* about the wave of the sound, or its variations, its length, etc.