In the past they provided Roku stickers etc in the packaging.
They ended up with the "Intel Inside" and "Creative Labs" and "Sound Blaster X-Fi" etc stickers from other past purchases - in a drawer somewhere, mostly forgotten and obviously unused.
You can probably find unsanctioned Roku T-shirts etc if you search online.
Roku probably figures they have enough branding/marketing on their actual products and in mindshare among the general public...