This is the easiest DIY I ever did and will probably ever do. It literally took me five minutes -though finding the perfect ribbon took me longer than that.
scissors (not pictured)
some sort of decorative ribbon (I am not sure what it is called in English)
glue for leather
nailpolish remover (aceton free)
1. Cut the ribbon.
2. Make sure the belt is oil free before applying the glue. I used nailpolish remover, but I am sure there is a 100 other ways to do this.
3. Apply the glue to the belt and add the ribbon.
4. Let it dry.