An idiomatic expression used when someone tries to hide something or deny guilt, but their awkward actions or overly defensive words make it completely obvious.
Based on a famous folk tale about a man named Zhang who buried his savings and put up a sign saying "no three hundred taels of silver buried here" to fool thieves, only to expose himself instantly. People use this phrase today whenever someone's clumsy attempt at covering up a mistake actually points straight to their guilt.