YSK: If you have signed up to be contacted about something and are no longer interested, you should tell the Telemarketer that instead of ignoring the call/just hanging up. This will lead to a lot less call spam.
from /r/YouShouldKnow
YSK: 如果你已经注册了某件事情并不再感兴趣，你应该告诉电话销售人员，而不是忽略电话/直接挂断。这将使垃圾电话减少很多。