It is not necessary, but amulets are customarily replaced once a year to ward off bad luck from the previous year. Old amulets are usually returned to the same shrine or temple they were purchased at so they can be disposed of properly. Amulets are commonly returned on or slightly after New Year’s. This way the shrine/temple visitor has a fresh start for the New Year with a new omamori.
It's the name of the temple it's from. Looks like it's from Ikimi, the oldest Tenmangu shrine in Japan.
By the way, it's considered to be a very common taboo to open omamori and check what is inside it.I open the omamori, and I found this ofuda