They may look like oranges to you, but they are tangerines.

In Chinese characters, the word "tangerine" has a similar (very close) pronunciation as the word "auspicious", so by giving them, or by having them, you are wishing or welcoming "auspicious" things, like prosperity, more money, promotions, etc, into your lives.

Did you ever look at them closley and realize that the tree is real with the tangerines wired on over the branches?
Would it be considered an insult to take one off and eat it?

Yes, I got closer because wondered how a tree could have so many and so evenly distributed, and noticed the wiring then.  The trees I saw were from 6 ft to 9 ft tall.

I have not seen anyone taking one or more, but I have seen some with signs that some were taken.  I guess if no one sees you, you can get away with taking some, and maybe if you are a laowai even if caught nothing will be said.

The tangerine trees that were given to me for the holidays were real trees with no wiring on them at all.  They came from down south, a greenhouse somewhere.  After I read this post, I checked all three of the trees very carefully.  Perhaps in some places, I don't doubt it at all, but not the ones sent to me.

Someone planted them.

dragons eat oranges, you must  put the orange trees out so that when the year of the dragon finally arrives after 12 long years, he will have something to eat. you dont want to wake up on the 23rd and find 700,000,000 breastless women. (do i really need to explain this one.... really ..... ok here goes .... the dragon did not find any oranges, so he ate the thing that closely resembled them) (resembled may be spelled wrong i've been drinking a lot recently)

Oranges are pretty much an every day item. When people I know buy oranges, or pick some themselves, they always offer a few to friends. As for trees, I have never heard of that.