clarify

This doesn't make sense at all. It's not grammatical and means nothing. To clarify is a transitive verb and means to make something clear. Eg :

The students obviously don't understand the use of the present perfect so I'll try and clarify it in the next lesson.

Here are some examples from the passive - notice that the object of the active verb (the "something") becomes the subject of the passive verb :

• This difference is readily clarified by referring to Table 1.
• [I]This connection was clarified by Smith and Smith (1922), who showed that ...
• Such legislation was clarified and extended from time to time thereafter. In 1913...
• ... when the norms were clarified and made more precise[/I]

It's not possible therefore to use it as a passive imperative which would need a personal subject. It means nothing.

I think what the writer means could be something like : Please note that this university is closed...
but as always, without the context it's impossible to interpret it accurately.

Excellent answer. Thank you.