You have probably noticed it on some garments that you bought.
It i a number, usually somewhere on the care labels, most likely with the letters RN# before it. As in the picture below.
An RN number or registered identification number is a number issued by the FTC (Federal Trade Commission), upon request, to a business residing in the U.S. and engaged in the manufacture, importing, distribution, or sale of textile, wool, or fur products.
However the above businesses are not required to have an RN#. They can use the RN in place of having their brand/company name on the main label which is required to be affixed to their products.
Applying for an RN # is free and it can be obtain online on the FTC website here. If providing an email address the application will then be processed in about 3 days and the number will be emailed to you. If applying via fax or regular mail it will take about 7-10 days.
Note: The information in the RN data system is based on the data that is being submitted by the registered companies. In other words, the registered companies is responsible to keep their info up-to-date.
Canada have their own revision of RN, its called CA and is being issued by the Competition Bureau and is geared for Canadian manufacturers, processors or finishers of a textile fiber product or Canadians engaged in the business of importing or selling any textile fiber product.