Sign post examples we often we use. The material is rough cedar. It's so easy to work with, lasts a long time and not too expensive.
By using a minimum of 2" thickness there is seldom any checking. Because the material is always damp it's necessary, when painting, to lay down a oil based barrier like Kils or Ronan block-out white in order to capture bleed through.
Even plain panels look better with larger posts.
Joe
www.normansignco.com