cat licking soap

we recently took in a stray. he's very friendly and has been roaming the
streets for at least 6 months from what people tell us. no one has claimed
him although we placed several local ads and called various shelters,
vets etc. he eats well and knows how to use the litter box. he's a really
beautiful cat with front double paws. the only problem other than his
restlessness (he's spayed from what we can tell), is that he jumps up on
the sink and licks the soap dish.

it can't taste that good and we've stopped him numerous times but he does
it again whenever he can sneak up on the sink. we've resorted to putting
the soap dish in the cupboard to keep it away from him. is this a sign of
anything beyond insanity?

thanks in advance.