Hi @Nighto - Thanks for bringing this up.
Here's our thinking on this. We can call it a policy.
1) We prefer to have photos free from clutter and markings. This includes watermarks, date/time markings, and commercial messages.
2) If having a sticker/logo/message on the disk that hides the photographer means that you can take photos (like the sponsorship scenario you mention) then you should go ahead and do that. It would be counter productive to prevent you from uploading just because of this.
So in short: We prefer NO logos/messages in the photos but we don’t want to prevent you from contributing photos with logos/messages.
Using a disk under the camera to hide part of the photographer or car underneath is generally a good idea and we should list that as a recommended solution.