Mount And Blade Best Performance How Do You Mount A Sign To A Tree?

How do you mount a sign to a tree? - mount and blade best performance

My family is a tree of more than 100 years. My mother wants a sign (approx. 12 "x12") for mounting on the tree to make a souvenir. The sign will be a Polyfab plastic. Has anyone any suggestions on how the sign on the tree mount at a reasonable cost, and brave the elements?