Usually, when you work in a company, in official letters (leave application, resignation and such), you mention that you are an employee at this company or your are leaving your position in this company and etc. What to write in place of "your company" or "this company" when it is not a company(not pvt ltd, llp or inc, or such) but a proprietorship?
The place I work in is a studio but it is not registered as a company in my best knowledge, but it is listed as a trademark (the name of the studio is not a company's name, the name is registered as a trademark.) and has a proprietor who is the boss.