What does it mean to throw two people's birthdays at the crossroads together?

Generally speaking, it is meaningless, just like a piece of paper thrown on the road.

Unless this paper is made, it may mean eliminating the sins of two people, because there are the most people at the crossroads, and they will be trampled. Stepping on it shows repentance, and being stepped on is to eliminate sin, but generally it is not done, but the threshold is donated to the temple.