  We study the behavior of the recently proposed "strange correlator" [Phys.
Rev. Lett. {\bf 112}, 247202 (2014)] in spin-1 Heisenberg antiferromagnetic
chains with uniaxial single-ion anisotropy. Using projective quantum Monte
Carlo, we are able to directly access the strange correlator in a variety of
phases, as well as to examine its critical behavior at the quantum phase
transition between trivial and non-trivial symmetry protected topological
phases. After finding the expected long-range behavior in these two symmetry
conserving phases, we go on to verify the topological nature of two-leg and
three-leg spin-1 Heisenberg antiferromagnetic ladders. This demonstrates the
power of the strange correlator in distinguishing between trivial and
non-trivial symmetry protected topological phases.
