The phrase "time is silent, birds are traceless" expresses people's helplessness and emotion about the flow of time, and also reminds people to cherish time and not to make it meaningless in meaningless disappearance.
"Time is silent" means that time can't speak, and it won't stop or go backwards because of people's prayers or stay. "Birds have no trace" means that birds fly across the sky without leaving any trace, just like time, once it passes, there will be no trace.