  The striped cuprate La$_{2-x}$Ba$_x$CuO$_4$ ($x=\frac18)$ undergoes several
transitions below the charge-ordering temperature $T_{co}$ = 54 K. From Nernst
experiments, we find that, below $T_{co}$, there exists a large, anomalous
Nernst signal $e_{N,even}(H,T)$ that is symmetric in field $H$, and remains
finite as $H\to 0$. The time-reversal violating signal suggests that, below
$T_{co}$, vortices of one sign are spontaneously created to relieve interlayer
phase frustration.
