that's their signal
( that ( 's ( their signal ) ) )
(ROOT (SBAR (WHNP (WDT that)) (S (VP (VBZ 's) (NP (PRP$ their) (NN signal))))))
That's their sign.
( That ( ( 's ( their sign ) ) . ) )
(ROOT (S (NP (DT That)) (VP (VBZ 's) (NP (PRP$ their) (NN sign))) (. .)))