I found this on my travels in Brookvale just north of Sydney. It's funny AND eye catching which on the surface isn't groundbreaking, but I wanted to make specific note of it and question exactly what makes it good.
Reverse psychology is always an interesting way to either catch attention or to illustrate a point. In this case the sign is apologetic in the first instance, which implies you are about to be disappointed. This however is not the case. You are immediately and pleasantly surprised by the fact that they are in fact open. There is a second layer here and it comes in the form of sarcastic irony. The sign is a lightweight portable A frame that is normally placed out the front of a business only when they are open. But this sign implies that they are closed by saying 'Sorry'. They could even go so far as to say "Sorry we are closed", and place the sign in a place that clearly illustrates that they are open. As clever as that idea is, I don't recommend it as the general populous are not sharp enough to figure it out.