Although the symbols differ, the most common one is paper in most of the countries. Paper is easy to tear and burn thus the meaning of the second anniversary symbol is rather clear - the family life is still very unstable.
This can be easily explained from the psychological point of view. The first two years full of positive emotions and passionate love however reveals lots of unexpected things about the spouses` character and habits. Besides the spouses get around trying to fulfil the plans the have made in their first year together. This process can be crucial for if the hopes and dreams of the first year do not come true than the arguments are inescapable. But if you love each other and do want to overcome all those difficulties you won`t blame your spouse for every fault, just on the contrary you will discuss everything and come to a compromise!
A baby birth is always a happy and one of the most precious moments in every family. In most families the first baby is born in their second year bringing lots of problems and fears. Elder relatives and friends should understand that it is important to support the family, calm them down if it is necessary and help them if is needed.
I also like the visual aspect of the 8th anniversary because it is similar to the infinity symbol which is a happy thing to associate with the connection you have with your husband or wife.