A red 'H' displayed on a stock symbol indicates that trading for that particular stock has been temporarily halted. This halt may occur for various reasons, including significant news announcements, regulatory concerns, or extreme volatility in the stock’s price. 

When a stock is halted, it signifies that no buying or selling can occur until the halt is lifted, enabling investors to process the information or circumstances that prompted the suspension of trading. It is essential for traders and investors to remain informed about the reasons behind a trading halt, as this can significantly influence the stock's future performance once trading resumes.