  A double moir\'e superlattice can be realized by stacking three layers of
atomically thin two-dimensional materials with designer interlayer twisting or
lattice mismatches. In this novel structure, atomic reconstruction of
constituent layers could introduce significant modifications to the lattice
symmetry and electronic structure at small twist angles. Here, we employ
conductive atomic force microscopy (cAFM) to investigate symmetry breaking and
local electrical properties in twisted trilayer graphene. We observe clear
double moir\'e superlattices with two distinct moire periods all over the
sample. At neighboring domains of the large moir\'e, the current exhibit either
two- or six-fold rotational symmetry, indicating delicate symmetry breaking
beyond the rigid model. Moreover, an anomalous current appears at the 'A-A'
stacking site of the larger moir\'e, contradictory to previous observations on
twisted bilayer graphene. Both behaviors can be understood by atomic
reconstruction, and we also show that the cAFM signal of twisted graphene
samples is dominated by the tip-graphene contact resistance that maps the local
work function of twisted graphene and the metallic tip qualitatively. Our
results unveil cAFM is an effective probe for visualizing atomic reconstruction
and symmetry breaking in novel moir\'e superlattices, which could provide new
insights for exploring and manipulating more exotic quantum states based on
twisted van der Waals heterostructures.
