  In this contribution, we present evidence for the occurrence of triangular
symmetry in cluster nuclei. We discuss the structure of rotational bands for
3-alpha and 3-alpha+1 configurations with triangular D(3h) symmetry by
exploiting the double group D'(3h), and study the application to 12C and 13C.
The structure of rotational bands can be used as a fingerprint of the
underlying geometric configuration of alpha-particles.
