For your trademark to be federally registered, you are required to provide proof (called a "specimen") to the U.S. Patent and Trademark Office (USPTO). The specimen you provide should be an actual example that clearly shows how the trademark is being used in connection with the goods and/or services you listed in your application.
If you are providing products, acceptable specimens include photographs of packaging labels, clothing tags or labels on containers that prominently display your trademark. Invoices, order forms, receipts, brochures, catalogs, press releases, business cards, and stationery are generally NOT acceptable specimens for products.
If you are providing services, acceptable specimens include a sign, brochure, advertisement, business card, stationary or website prominently displaying your trademark in connection with the services you've listed in your application. The specimen must include a reference to the service, not just the trademark by itself. For example, a business card simply printed with the trademark "Sunny Real Estate" would likely not qualify, whereas one printed with "Sunny Real Estate" and "Sales Training Services" below it could qualify. Printer's proofs for advertisements or news articles about your services are generally NOT acceptable specimens for services.