SIC Codes are no longer assigned by the US Government as they have been replaced by NAICS (North American Industrial Classification System). However, there are many agencies and organizations both government and otherwise that do still utilize these codes for a variety of reasons. Some will assign you a code themselves, though in most cases, you will be asked to provide your code.
An example of a company that may assign you an SIC Code is Dun & Bradstreet. If more than one SIC Code is assigned to a company by D&B, the first one listed is the primary line of business. The remaining codes, if any, comprise at least 10 percent of the firm’s annual revenue. These codes can be updated by using the D&B iUpdate Service.
An example of a government agency that uses SIC Codes is the U.S. Securities and Exchange Commission. The SEC does not assign codes, however, when a company registers their IPO, they will select an SIC code by assessing its primary source of revenue. The SEC and other agencies that use these codes can usually be reached if you need to alter the code they’re using on your record.