815 ILCS 395/3
If there is any quality mark printed, stamped, or branded on the article itself, there must also be printed, stamped, or branded on the said article itself the following mark, to-wit: A trade-mark duly applied for or registered under the laws of the United States of the manufacture of such article; except that if such manufacturer has sold or contracted to sell such article to a jobber, wholesaler, or retail dealer regularly engaged in the business of buying and selling similar articles, this provision shall be deemed to be complied with if there is so marked on the said article the trade-mark duly registered under the laws of the United States of such jobber, wholesaler, or retail dealer, respectively; and in such event there may also be marked on the said article itself numerals intended to identify the article, design, or pattern: Provided, however, that such numerals do not appear or purport to be a part of the quality mark: Provided further, that they are not calculated to mislead or deceive anyone into believing that they are partly of the quality mark.
815 ILCS 395/3