Good question! 

I won't get into the nuance of what that certificate is all about. I'd address the question in the title -do you say certificate 'about' or 'of'.

Though both convey the same meaning, in my opinion, in most of the cases, when you say 'certificate about...' it takes a phrase. I mean to say that there could be some explanation of what that certificate is all about, and not just one word.

For instance a doctor's certificate about the applicant's fitness for the job 

On the other hand, 'certificate of' is short and terse. It directly says what is that certificate with no explanation. 

Say - a certificate of registration/membership/excellence/participation...and so on

But I repeat, both conveys the same meaning and there's no strict rule about what I said. It's just my minute observation. 

Do you say certificate about or certificate of?
I'm thinking in particular of dictionaries or illuminated bibles being displayed on these stands, which are at least waist-high on a standing person, constructed of wood.  Is there a particular word for this, other than "book stand"?
