Some gold selling spammer been bothering you? Constantly spamming you with their message? Each time you block, the next day they are on a new character? Well the way they find names to whisper is by searching. So if you remove yourself from search, they won't be able to find out your name.
This will work for 99% of the whisper spam.
Like the image above shows, go to settings and then Chr menu. Tick "Search Denied" and save. Now you have been removed from Searches so they should hopefully stop.