negative value of signals
I believe you are talking about soundwaves only, so I'll approach the answer from there.

The instant values a signal takes don't tell much about the sound it may generate. If a signal is zero at a certain instant $t_0$, it doesn't mean that at that moment there is silence. A single sample can't represent any sound because only oscillations can generate sound. I hope you see why a single sample can't possibly represent  an oscillation of any kind.

Take for example a perfect sinewave. The signal $x(t)=\sin(t)$ is $0$ for infinite values of $t$, but the sound you hear is nonetheless uniform and constant. Also, it takes both positive and negative values, but the note you hear is always the same.

If a signal is $0$ for a given period of time though, then for that interval there will be silence indeed. In fact, if a signal is constant for a given period of time (not necessarily $0$), you will hear no sound at all (but you would be wasting power nonsensically).

In a nutshell, the instant values of a signal represent no sound whatsoever. It's the change over time of these values that can represent and generate sounds.