Actually a very easy solutions can solve the problem.
Issue Prostitute permit to work in Singapore. There are General
Domestic Permit, Worker Permit, "P" pass .... why on a "Pro"
permit?
MOM can tax them very high like $2000~4000 a month. Permit can have
a very short terms, like 3 months. They must pass the health test
& "skill" test.
Good points: More $ comes into help Singapore, Sex health is more
controlled, Lesser social problems, New faces for customer = more $
for Singapore, Lesser work for police to catch those without
permits, Other options of permit is not abused .....
Bad points: it's a bad name for Singapore, but equally bad if
social problems with PRC without proper permit working as
Prostitutes or husband snatching family breaking women.
I believe if there is a option open for people, they will not take
the risk of being caught & unprotected.