Final answer:
Percy attempts to keep a low profile on the train to avoid drawing attention to his luxurious lifestyle and his family's wealth, which are parts of his life that require discretion and secrecy.
Step-by-step explanation:
In the context provided, Percy aims to keep a low profile on the train because he deals with aspects of his life that are not meant for public knowledge or attract unwanted attention. From having a special limousine that shouldn't be seen by others on the train or the people in Fish to confiding about his father's immense wealth, Percy's actions suggest that he is part of an exclusive and secretive society, where discretion is paramount.
The use of the limousine as a 'station wagon', his casual mention of his father's wealth, and the need to avoid being trailed indicate a lifestyle of privacy and hidden luxury. These examples highlight Percy's need for secrecy and the importance of maintaining a low profile in public settings, which is a consistent theme throughout their journey and interactions.