  Recent experiments show strong evidences of nematic triplet superconductivity
in doped Bi$_2$Se$_3$ and in Bi$_2$Te$_3$ thin film on a superconducting
substrate, but with varying identifications of the direction of the $d$-vector
of the triplet that is essential to the topology of the underlying
superconductivity. Here we show that the $d$-vector can be directly visualized
by scanning tunneling measurements: At subgap energies the $d$-vector is along
the leading peak wave-vector in the quasi-particle-interference pattern for
potential impurities, and counter-intuitively along the elongation of the local
density-of-state profile of the vortex. The results provide a useful guide to
experiments, the result of which would in turn pose a stringent constraint on
the pairing symmetry.
