For a certain class of Markov processes, the $\lambda$-capacitary measure $\pi^\lambda_S$ of a semipolar set $S$ has the following property under a mild condition: A subset $B$ of $S$ is polar if and only if $\pi^\lambda_S(B) = 0$.
"A Note on Capacitary Measures of Semipolar Sets." Ann. Probab. 17 (1) 379 - 384, January, 1989. https://doi.org/10.1214/aop/1176991517