Sorry, it was just something a Chinese collector friend told me. I showed him a set of short shuang jian, just as you are describing with the tortoise shell. I had thought it a particularly interesting set because its provenance was a Chinese family in Sumatra, and I liked it as an example of cultural migration. He mentioned that they were frequently given as wedding presents because the double sword was good luck for the marriage.
Unfortunately the story is apocryphal, but it does seem plausible. As a counter argument, my Chinese Indonesian friends do not think a knife as a gift is good luck. They would be uncomfortable with any sort of sword as a wedding present.
