https://www.sec.gov/answers/qadded.htm
"Q" Added To Stock Ticker Symbol
When a company is involved in bankruptcy proceedings, the letter "Q" is added to the end of the company's stock ticker symbol. In most cases, when a company emerges from bankruptcy, the reorganization plan will cancel the existing equity stock and the old shares will be worthless. Given that risk, before purchasing stock in a bankrupt company, investors should read the company's proposed plan of reorganization. For more information about the impact of bankruptcy proceedings on securities, please read our online publication, Corporate Bankruptcy.