  Moir\'e heterostructures are rapidly emerging as a tunable platform to study
correlated electronic phenomena. Discovery of exotic quantum phases in moir\'e
systems requires novel probes of charge and spin order. Unlike detection
schemes which average over several moir\'e cells, local sensors can provide
richer information with greater sensitivity. We study a
WSe$_2$/MoSe$_2$/WSe$_2$ heterotrilayer which hosts excitons and electrons in
distinct moir\'e lattices, and show that localized dipolar excitons are
sensitive proximity charge sensors, uncovering numerous correlated electronic
states at fractional fillings of the multi-orbital moir\'e lattice. In
addition, the emission polarization can reveal the local electronic spin
configuration at different fillings. Our results establish dipolar excitons as
promising candidates to study emergent quantum matter and quantum magnetism in
moir\'e crystals with higher spatial resolution.
