branding watermark

The branding watermark (subscribe button) that appears bottom right doesn't seem to have any purpose if viewing on a mobile device as you can't press it anyway! Either in full screen or not. Because if you aim for and click bottom right it simply pulls up the video progress scroll bar overlay...

At the channel branding page on YT one may upload a custom graphical icon being displayed while a video is being watched. Clicking this icon while the video is watched leads to the viewer subscribing the respective channel. In an instruction video floating around the Youtubes (forgot which of...