https://github.com/jupyter/design contains Jupyter logos (and an nbviewer badge) along with brand guidelines.
The only reference I’ve found to an official jupyterhub logo is https://github.com/jupyterhub/jupyterhub/issues/1703#issuecomment-400629567
The issue on how to cite Jupyter is still open https://github.com/jupyter/jupyter/issues/190
I think it’d be helpful if these and any other related media could all be linked in one place so it’s easy to find what you need for presentations, reports, etc. Google does a reasonably good job but it’d be nice if this could be somewhere “official”.