I am looking for the meaning of the Greek Key Symbol. If anyone can help me I would appreciate it.

The reason is that I have been looking for my Fiancé a wedding band and this is a symbol I have come across a few times on some of the rings and I want to know what it means befroe I settle with it. I am looking for something special and meaningful. Something Unique, If anyone has any ideas PLEASE let me know. I only have 1 month till the wedding, and I still can't decide.:)