  We prove a case of a positivity conjecture of Mihalcea-Singh, concerned with
the local Euler obstructions associated to the Schubert stratification of the
Lagrangian Grassmannian LG(n,2n). Combined with work of
Aluffi-Mihalcea-Sch\"urmann-Su, this further implies the positivity of the
Mather classes for Schubert varieties in LG(n,2n), which Mihalcea-Singh had
verified for the other cominuscule spaces of classical Lie type. Building on
the work of Boe and Fu, we give a positive recursion for the local Euler
obstructions, and use it to show that they provide a positive count of
admissible labelings of certain trees, analogous to the ones describing
Kazhdan-Lusztig polynomials. Unlike in the case of the Grassmannians in types A
and D, for LG(n,2n) the Euler obstructions e_{y,w} may vanish for certain pairs
(y,w) with y <= w in the Bruhat order. Our combinatorial description allows us
to classify all the pairs (y,w) for which e_{y,w}=0. Restricting to the big
opposite cell in LG(n,2n), which is naturally identified with the space of n x
n symmetric matrices, we recover the formulas for the local Euler obstructions
associated with the matrix rank stratification.
