erm i found some problem... when playing career mode the original existing sign will change with the ride (as the ride broke it will change automatically to "broken down")
and when click the "change whether the ride has a sign over its queue" it will show out or disappear...
but i cant apply it to new bulid rides... how to 'connect' the sign to the ride?

You have to create a queue line and add it to the ride, make sure the sign on queue line entrance feature is on.