  We describe a novel use of the Dalitz plot to probe CP symmetry in three-body
modes of $B$ and $D$ mesons. It is based on an observable inspired by
astronomers' practice, namely the significance in the difference between
corresponding Dalitz plot bins. It provides a model independent mapping of
local CP asymmetries. We illustrate the method for probing CP symmetry in the
complementary cases of B decays, where sizable or even large effects can be
expected, yet have to be differentiated against leading Standard Model
contributions, and $D$ decays, where one cannot count on sizable effects, yet
has to deal with much less Standard Model background.
