b. Lamborghini’s mark is not weekend by third-party use because the third parties’ marks are not in the Lamborghini’s market of producing luxury sports vehicles. The presence of third-party registered marks alone is not enough to substantially weaken the strength of the plaintiff’s mark. Homeowners Grp., Inc. v. Home Mktg. Specialists, 931 F.2d 1100, 1108 (6th Cir. 1991). A third-party mark weakens a senior mark when the third parties “use the marks in the relevant market.” Kibler