I was recently in china visiting my girlfriend and at midday whilst she was at work air raid sirens went off at every police station in the city for nearly 5 minutes.
I asked my girlfriend what it was for and she replied that it was the Dongguan People's safety day and that she nor any of her colleagues could explain anymore than that it was the anniversary of an event that involved a Japanese massacre on that day in 1938 in the area.
I have spent quite a lot of time looking this up online and I cannot find a single thing about a massacre on this day in that area. So I suppose the thing I want to know is what happened to make this a memorial Day.
Nothing so dramatic as a massacre. As far as I know, 20/11/1938 is merely the date when Japanese troops occupied the city of Dongguan in the Second Sino-Japanese War. The sirens are in commemoration of this event.
Source:
Zuo, Shuang-wen. Huanan kangzhan shigao [History of the Anti-Japanese War in South China]. Guangzhou: Guangdong gaodeng jiaoyu chuban she, 2004.