  In few-body physics, Efimov states are an infinite series of three-body bound
states that obey universal discrete scaling symmetry when pairwise interactions
are resonantly enhanced. Despite abundant reports of Efimov states in recent
cold atom experiments, direct observation of the discrete scaling symmetry
remains an elusive goal. Here we report the observation of three consecutive
Efimov resonances in a heteronuclear Li-Cs mixture near a broad interspecies
Feshbach resonance. The positions of the resonances closely follow a geometric
series $1$, $\lambda$, $\lambda^2$. The observed scaling constant $\lambda_{\rm
exp} = 4.9(4)$ is in good agreement with the predicted value of 4.88.
