Counterfeit currency

I've never been in any country before where EVERY bill is carefully scrutinized by EVERYONE. This leads me to believe that counterfeit currency is a big problem here. Everything from a RM20 (US$3) to a RM100 (US$15) is checked.

I've only changed money at two banks in China. Yesterday, a taxi driver refused to take a RM100 bill because he said it was fake. I didn't think too much of it. I gave him another bill and pocketed the rejected bill and forgot all about it. Then I went to The Bund Brewery and got the same bill returned. The bill is a little lighter in colour. I should have suspected something because there is a little smiley face stamped in the lower left corner. When I checked all of the bills that I got from the banks, I found a second bill with the same smiley face in the lower left corner, so I guess that makes two fakes. This is a little irritating because I find it hard to believe that the banks didn't catch this, but it's only US$30 so I'm not going to do anything but save them. At any rate, I'm not sure which bank gave them to me, so there isn't anything that I can do.
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Update: I was looking at all of the bills in my wallet (different denominations) and about half of them have a little smiley face (actually, on closer inspection, a smiley face with no eyes). So...I actually have no way of telling except by looking at the color, but, some of the older bills are so dirty and faded, I don't know how anyone can tell. The whole thing is quite perplexing. I'm going to keep the bill no one wants separate and hope that the second bill is fine. Hmmm.