In general, a Chinese custom. When your eating out of a bowl and you want to stop eating. You cant leave your chopsticks in a bowl. Its rude and bad luck because it looks like a tombstone. So you have to rest them on the edges of the top of the bowl or in the chopstick holder.
The informant heard this when she was studying abroad in Beijing, China. She was with her Chinese language partner. The custom is commonly known and people are brought up know this. She says that she only would follow the custom to be polite and make the people feel comfortable but did not believe it to be true in any way.
Chinese culture has a lot of customs and superstitions regarding death. I would never think it to be superstitious to leave my chopsticks in a bowl, but many Chinese would see that as a bad practice. The concept of death transcends into a majority of Chinese folkloric practices. I find this to be very interesting because I feel like eating and chopsticks has nothing to do with tombstones and death. But, this is a superstition passed down from generation to generation and people do not want bad luck.