SOLD SIGNS???

What is the point of SOLD signs? I don't see the point of these ridiculous things. I fully understand FOR SALE signs, they are there for a purpose. They inform anyone and everyone who passes that house that its for sale. The FOR SALE sign screams at you. it says "oi mush, come here and look at me, I'm for sale". SOLD SIGNS are just rude. They say "Oi mush, do you want to buy me? well you can't, so jog on. If you wanted me you should come over last week when I was available. "I fail to see why estate agents put these SOLD SIGNS up. What will be next? FAMILY MOVED IN signs. To me, I think its just estate agents showing off, "look at me, I had a house for sale", I put up a FOR SALE sign and I sold. Now I have erected a SOLD SIGN" aint I great? No you are just a smug git. la la la.