Trademark use must be substantially exclusive
Timberland filed a trademark application for the design and appearance of its lace-up boots (Application Ser. No. 86634819 (May 19, 2015)). The application was rejected, and the Trademark Trial and Appeal Board (TTAB) affirmed (See In re: TBL Licensing, LLC, No. 86634819 (Apr. 2, 2021)).
One of the reasons the USPTO Trademark Attorney rejected the application was that Timberland failed to show that its use was substantially exclusive. The TTAB found that because there were many very similar third-party boots Timberland failed to show sufficient evidence that Timberland was policing its mark.
Image is a specimen submitted to the USPTO on May 19, 2015 (link)