Look at the way well-known brands use their company name as a trademark or services mark. They usually do not include an entity descriptor–e.g. Inc., Corp., Ltd., or LLC–in those brand usages. For example, the company behind the Starbucks brand is “Starbucks Corporation.” However, you rarely see the word “corporation” used in connection with Starbucks when Starbucks is used as a trademark. Instead, “Starbucks Corporation” is mostly used in the fine print when referring to the corporation rather than the brand, such as in their copyright notice.
One reason for that is marketers probably do not want unnecessary legal language cluttering up their beautifully crafted names/brands. Another reason is that trademark law somewhat discourages the inclusion of entity descriptors in trademarks.
The Lanham Act provides for the federal registration of trademarks and service marks, but not trade names. Under the Act, a “trade name” is “any name used by a person to identify his or her business or vocation.” 15 USC 1117.
The name of a business can act both as a trade name and a trademark/service mark. However, the Trademark Trial and Appeals Board has said that the inclusion of an entity descriptor in the mark to be registered “is a factor which frequently leads to a finding solely of trade name use, especially when the name appears in close proximity to a corporate address.” In re Univar Corp., 20 USPQ2d 1865, n.6 (TTAB 1991); TMEP 1202.01. Other factors that can lead to a conclusion that the mark applied for is only a trade name is if the mark is only used in a corporate address and is the same color, size, and font as the remaining or surrounding text. In re Diamond Hill Farms, 32 USPQ2d 1383 (TTAB 1994).
If you search the trademark database at the USPTO, you will find many registered trademarks containing entity descriptors. Therefore, many applicants have been able to show that their business names function as a trademark/service mark. Further, the mark you seek to register must match the mark you actually use in your business.
However, since an entity descriptor is not required in a trademark, and since a trademark might be marginally stronger without a entity descriptor, the entity descriptor is often not used in a trademark.