Wishing Well banner?

I am helping with my friend's baby shower wishing well.  It is supposed to be an exclusive "diaper wishing well".  Instead of creating some type of box to put the items in, I thought it might be nice to utilize a large windowseat she has in her main living room as the spot for the "well" gifts (the shower is taking place at the mom-to-be's house).  This way we can display the gifts, big diaper boxes, and a diaper cake that I know a few people are creating.  However, I wanted to make a nice sign or banner to go across the window, that says "Wishing Well", and then this area of the room will serve as part fo the shower decor.  WDYT?  How can I create a banner like this, inexpensively?