Interpreting the symbol
Stock symbols are unique identifiers assigned to each security traded on a particular market. For example, AAPL is for Apple Inc.; OODH is for Orion DHC, Inc.; and HD is for Home Depot, Inc. A stock symbol can consist of letters, numbers, or a combination of both, and is a way to uniquely identify that stock. The symbols were kept as short as possible to reduce the number of characters that had to be printed on the ticker tape, and to make it easy to recognize by traders and investors.
The allocation of symbols and formatting convention is specific to each stock exchange. In the US, for example, stock tickers are typically between 1 and 4 letters and represent the company name where possible. For example, US-based computer company stock Apple Inc. traded on the NASDAQ exchange has the symbol AAPL, while the motor company Ford's stock that is traded on the New York Stock Exchange has the single-letter ticker F. In Europe, most exchanges use three-letter codes, for example Dutch consumer goods company Unilever traded on the Amsterdam Euronext exchange has the symbol UNA. While in Asia, numbers are often used as stock tickers to avoid issues for international investors when using non-Latin scripts. For example, the bank HSBC's stock traded on the Hong Kong Stock Exchange has the ticker symbol 0005.
Symbols sometimes change to reflect mergers. Prior to the 1999 merger with Mobil Oil, Exxon used a phonetic spelling of the company "XON" as its ticker symbol. The symbol of the firm after the merger was "XOM". Symbols are sometimes reused. In the US the single-letter symbols are particularly sought after as vanity symbols. For example, since Mar 2008 Visa Inc. has used the symbol V that had previously been used by Vivendi which had delisted and given up the symbol.
To fully qualify a stock, both the ticker and the exchange or country of listing needs to be known. On many systems both must be specified to uniquely identify the security. This is often done by appending the location or exchange code to the ticker.
Although stock tickers identify a security, they are exchange dependent, generally limited to stocks and can change. These limitations have led to the development of other codes in financial markets to identify securities for settlement purposes. The most prevalent of these is the International Securities Identifying Number (ISIN). An ISIN uniquely identifies a security and its structure is defined in ISO 6166. Securities for which ISINs are issued include bonds, commercial paper, stocks, and warrants. The ISIN code is a 12-character alpha-numerical code that does not contain information characterizing financial instruments, but serves for uniform identification of a security at trading and settlement.
The ISIN identifies the security, not the exchange (if any) on which it trades; it is therefore not a replacement for the ticker symbol. For instance, Daimler AG stock trades on twenty-two different stock exchanges worldwide, and is priced in five different currencies; it has the same ISIN on each (DE0007100000), though not the same ticker symbol. ISIN cannot specify a particular trade in this case, and another identifier, typically the three- or four-letter exchange code (such as the Market Identifier Code) will have to be specified in addition to the ISIN.
Symbol for stock market indices
While usually a stock ticker identifies a security that can be traded, stock market indices are also sometimes assigned a symbol, even though they can generally not be traded. Symbols for indices are usually distinguished by adding a symbol in front of the name, such as a caret (^) or a dot. For example, Reuters lists the Nasdaq Composite index under the symbol .IXIC.