Can Anonymous Letters Be Signed?

A senior girl in high school continues to receive anonymous love letters during her graduation season. The handwriting is the same as the diary of a senior who died in a car accident seven years ago. She traced it and found that it was written by the senior's mother imitating her son's handwriting - it turned out that the senior was killed when he rushed to meet her for the first time, and the mother continued to use love letters to continue her son's first love that could not begin. In the end, the two hugged each other in the rainy season classroom and read the last letter for the forever seventeen-year-old boy.