The term "ticker symbol" refers to the symbol used to denote a stock, Mutual Fund or ETF; all of which trade on the stock market. Oil trades on the commodities market and can be found on any number of web sites which display commodities prices. You will find headings for different types of oil as well including light crude and heating oil. You can buy an oil tracking ETF on the stock market. Use symbol "OIL", or "USO".
I'm not sure if the iPhone Stocks App links directly to the commodities market so the results you're seeing may just be the ETFs or specific companies.