Okay, okay, to those of you who gave up, here is the answer. To those who still want to find out for yourselves, skip this post. (^^)
If you walk along Pagoda Street, you will see this door which is part of the Chinatown Heritage Museum. If you have been to the museum, you might not notice it as you don't go in through this door. (^^) If you have yet to visit the museum, go and visit. It is certainly worth your 2-3 hours there.