Victor Mair has a post at the Log about the use of pinyin in China without either translation or characters; he begins:
I just passed through security at the Xi’an airport (in northwest China) and was surprised to have my belongings searched by a young woman on whose snazzy black uniform, instead of an ID number as a regular worker would have, there was a label that said only SHIXI (“in training; practice”), with no trace of the corresponding characters 实习 anywhere about her. When I read out the pinyin with correct pronunciation and indicated that I knew immediately and exactly what it meant, the young woman and her co-workers were obviously pleased that I could do so.
Even more thought provoking is the fact that many Chinese police cars and uniforms have written on them GONGAN (“public security”) rather than “police”, and sometimes not even 公安.
It’s an interesting phenomenon with a number of possible explanations, currently being hashed out in the comment thread. I am, of course, interested in your thoughts.