You can file a Fictitious Firm Name form with the Business License Division. Visit carsoncity.gov/businesslicense for more details. 

A Fictitious Firm Name is a legal document showing the operating name of a company, as opposed to the legal name of the company. If you're starting a sole proprietorship or a partnership, you have the option of choosing a business name or dba (doing business as) for your businesses. This is known as a fictitious business name.