Did anyone but me ((Which I doubt)) notice that when Matt woke up there was a "Welcome to Costa Verde" sign behind him.

I noticed it

It was a nice touch to the paintings and a bit ironic, seeing as those signs welcome and greet visitors into what's supposed to be a warm (lol) and prosper community.

I also found it curious that they're in a desolate place with nothing around and then there's a "Welcome to Costa Verde" sign, first thing I think is Time Warp or something that cause Costa Verde to be destroyed.

Nice little hint on where the painting takes place. Remember back near the end of season one, Sylar had happened to include the words "KIЯBY PLAZA". Yes, he wrote a backwards R. Seems a bit odd for the painters to include that, though Usutu's welcome sign fit better as being part of the physical world the painting represents.