A key factor in any likelihood of confusion analysis under Section 2(d) involving the similarity of marks is the strength or weakness of the registered mark asserted against the applied-for mark. See, e.g., Heil Co. v. Tripleye GmbH, No. 91277359, 2024 TTAB LEXIS 494, at *47 (“Because it affects the scope of protection to which it is entitled, we commence by addressing the strength or weakness of Opposer's registered … mark.”). 

Two prongs of analysis for a mark's strength under sixth DuPont factor are “conceptual strength and commercial strength.” Spireon, Inc. v. Flex Ltd., 71 F.4th 1355, 1362 (Fed. Cir. 2023) (citation omitted).14 “Conceptual strength is a measure of a mark's distinctiveness . . . and distinctiveness is often classified in categories of generally increasing distinctiveness[:] . . . (1) generic; (2) descriptive; (3) suggestive; (4) arbitrary; or (5) fanciful.” Id. (citation and quotation and quotation marks omitted). “Distinctiveness is relevant to a mark's overall strength in the likelihood of confusion analysis.” Id. (citation omitted).

Where a registered mark is shown to be “highly suggestive,” it may be entitled to an abbreviated scope of protection because that mark is less likely to cause confusion over source identification as opposed to “more fanciful” marks. Spireon, 71 F.4th at 1362-63. But, in the context of ex parte prosecution, arguing that a registered mark is “descriptive” would be an impermissible collateral attack on the registration. See In re Dixie Rests., Inc., 105 F.3d 1405, 1408 (Fed. Cir. 1997); In re Nat'l Data Corp., 753 F.2d 1056, 1059-60 & n.8 (Fed. Cir. 1985). With respect to TTAB jursiprudence, an ex parte appeal is not the proper forum for such allegations; instead, they should be brought in a formal cancellation proceeding. See, e.g., In re Calgon Corp., 435 F.2d 596 (CCPA 1971).

The conceptual strength of GUN FU was at issue in an appeal of a Section 29d) refusal of the applied-for SPINE – THIS IS GUN FU mark for “downloadable computer games software,” “home video game machines,” “hand-held computer games equipment, namely game consoles,” and “providing online, interactive multi-player computer games” in view of the registered GUN FU mark for “Downloadable computer game software via a global computer network and wireless devices.” In re Nekki Limited, Ser. No. 98767008 (TTAB Apr. 22, 2026). 

The TTAB rejected applicant assertion that registered GUN FU mark was “descriptive” as an impermissible collateral attack on the registration, noting that such a challenge instead would need to be brought in a formal cancellation proceeding directly against the registration. 

Nonetheless, the TTAB did consider whether the cited mark was “suggestive.” Two websites were made of record. First, a TV Tropes website described “Gun Fu” as “a catch-all term for stylized firearm-based combat styles in fictional visual media that combines martial arts with guns.” Second, the Wikipedia website defined “Gun Fu” as “hand-to-hand combat and traditional melee weapons in a roughly 50/50 ratio [which] can be seen in Hong Kong action cinema, and in American action films influenced by it.” 

     Applicant's evidence helps demonstrate that some of the public will understand “Gun Fu” as evoking a genre of “fictional visual media that combines martial arts with guns,” as the TV Tropes website explains. The Wikipedia entry also helps show “Gun Fu” has a similar meaning in connection with films. In the context of media combining the use of guns with martial arts, it is certainly strongly suggestive of the subject matter. As such, Applicant's evidence, albeit from only two websites, is probative and tends to show the registered mark has some conceptual weakness

Thus, while the cited registered mark, GUN FU, was inherently distinctive, it “has some conceptual weakness when used in connection with media or subject matter that involves guns used in martial art combat.” But this was not enough to overcome the Section 2(d) refusal to register the applied-for SPINE – THIS IS GUN FU mark. 

For example, the TTAB noted there nonetheless were “strong visual and aural similarities” between the mark because the registered mark GUN FU was entirely “subsumed” within Applicant's mark, SPINE – THIS IS GUN FU. 

Thus, while the initial part of Applicant's mark looks and sounds different from Registrant's mark, the latter phrase THIS IS GUN FU is very similar in those aspects of the marks. Importantly, the words THIS IS further draw attention to and directly emphasize the GUN FU element.

While the initial first word of the applied-for mark, SPINE, was an arbitrary element that “generally will play a stronger role in the mark's overall commercial impression”; the TTAB found that “the following phrase THIS IS GUN FU, separated by a hyphen, helps convey a fundamental similarity in terms of the marks' source-indicating commercial impressions.” 

This is because the phrase THIS IS GUN FU is likely to be understood by consumers as projecting a connection or source-affiliation with Registrant's GUN FU branded goods. In other words, consumers familiar with Registrant's mark, GUN FU, are likely to mistakenly believe Applicant's goods and services, being sold under SPINE – THIS IS GUN FU, are a version or extension of the Registrant's goods. See, e.g., Double Coin Holdings, 2019 TTAB LEXIS 347, at *23 (“ROAD WARRIOR looks, sounds, and conveys the impression of being a line extension of WARRIOR.)”

Furthermore, the marks' respective goods and services were legally identical or otherwise “have a close intrinsic relationship” that would “target the same class of consumers” and presumably be “found in the same trade channels.” 

Accordingly, the TTAB affirmed the Section 2(d) refusal of the SPINE – THIS IS GUN FU mark in view of the registered GUN FU mark.