After several years of accidentally banging my head on a low-hanging support beam whenever I went down the stairs to the basement, the final straw was when I was cleaning out the camper and I banged my head on the overhead cabinet three times while sweeping the floor.  After a lot of cussing, I went into the house and made this sign to call attention to, “You WILL hit your head against this, HARD, unless you duck!” and posted it in the camper and the basement stairway.