During a short wait in a garage, I caught sight of this notice lying on the floor in a corner. 

Volkswagen, I would say at least 40 years ago.

A message that is a little dusty in form; perhaps, in recent years, forgotten by some; yet fresh, crystal clear, effective. Universal.

It is your User who gives value to your work.

Try to understand him in order to address him with sincere helpfulness and honest competence: in this way you play your role well.