I suppose that some unincorporated persons might be tempted to add "Inc." to give an impression of corporality to their activities. Although Nevada is famously lenient to many vices, impersonating a corporation is not one of them. NRS 78.047 imposes a fine of up to $10,000 on anyone that is:
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purporting to be a corporation organized and existing under the laws of Nevada but has willfully failed to file with the Secretary of State articles of incorporation;
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doing business in Nevada as a corporation organized and existing under the laws of Nevada but has willfully failed to file with the Secretary of State articles of incorporation; or
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doing business in Nevada as a corporation organized and existing under the laws of Nevada while the corporation is in terminated status.
Secretary of State
Commercial Recordings Division
Attn: Business Compliance
202 North Carson Street
Carson City, Nevada 89701
NAC 78.405. The regulations specify the information that must be included with the report. The regulations require that a report must be on a form prescribed by the Secretary of State, but I could find no such form on the Secretary of State's website.
Update: The Nevada Secretary of State's office has informed me that the form is available here.