Hello. 

You can select your own SIC code.  The best thing is to first check with your accountant to see if one has been selected for you in a previous tax return.  If not, your primary SIC code description that which generates the highest revenue for your company at a specific location. 

An SIC code is 4 digits. You may see 4 digits followed by a dash with two additional numbers.  Strictly use the first 4 digits to establish your SIC code.

See this link below to help identify the SIC codes by keyword:

http://www.osha.gov/pls/imis/sicsearch.html

You can also register your business for Free by SIC code:

www.siccode.com - The Worldwide Business Directory

SICCODE.com - The Worldwide Business Directory

SIC Codes / NAICS Codes

Standard Industrial Classification System

North American Industrial Classification System

FREE Registration - FREE Company Listings

Standard Industrial Classification (SIC) codes are 4 digit numerical codes assigned by the US govt. to business establishments to identify the primary business of the establishment. The classification was developed to facilitate the collection, presentation and analysis of data; and to promote uniformity and comparability in the presentation of statistical data collected by various agencies of the federal government.

Please visit http://www.siccode.com for more information and helpful resources.