The Standard Industrial Classification (SIC) code system was for use by statistical agencies of the government in the statistical reports of government agencies like the Office of Management and Budget and the Occupational Safety and Health Administration (OSHA). A business did not apply for the code like an Employer Identification Number, nor was a code assigned to a particular firm. After November 2004, SIC Codes were no longer assigned to industries, since the government had adopted the North American Industrial Classification System.
Find out what the business under study does or did: does it make cars? Does it make car parts? Does it wholesale car parts? In 1997, the U.S. Government, in conjunction with the Canadian and Mexican Governments, developed the North American Industrial Classification System as a more comprehensive means of describing the activities of a business. Old SIC codes were converted as databases were updated and,in November, 2004, the United States stopped assigning new SIC codes. As of 2004, businesses are now described by the NAICS code only. Historical data using SIC codes is still available from the U.S. Department of Labor, as is the NAICS code information (see Resources, below)
Go to the U.S. Department of Labor website that lists SIC Codes (see Resources, below). You must enter either an SIC code or a keyword. If you are searching for an SIC code, you must either enter a keyword which describes the type of business activity, such as "Miscellaneous Retail Stores, Not Elsewhere Classified," since the SIC describes business activities rather than name particular businesses, or you must use the 1987 SIC Manual, available through the link at the top of the same web page.
Use the SIC Division Structure on the first page of the virtual 1987 SIC Manual to find the industry and sub-classification of the kind of business you are researching, then click that link for more information. If, for example, you know that the business category you want to research is art dealers, go to "Division G, Retail Trade", and find the Major Group that most closely resembles the activities of the firm you are researching. Clicking on Major Group 59, for example, will take you to Miscellaneous Retail, which includes drug stores, liquor stores, used goods shops, fuel, and miscellaneous stores "not classified."
Find the comparable NAICS code by going to the NAICS page at the U.S. Department of Labor (see Resources, below), if desired.