My friend found a cache where there was a birthday card inside. It is a wonderful idea! To sign a birthday card and then when that “log” is full, it gets to be given to someone for their birthday. 

Here are some links to birthday themed goecaches:

His premise is that  “You must leave something you would put in a birthday card”

When you type in “Birthday” you get 330 hits!

And one you are supposed* to log on your birthday!