We are working on a simular project.
My guess is that you need to use the XML component and have a backend service that uses the EWS framework to pull information from Exchange and save it to XML
As I am not allowed to post external links (Can't figure out why someone would place such a stupid rule on this forum) I am afraid that you will have to take the long way around.
on MSDN at microsoft you can search for the EWS API, If all else fail, lets try and find a way you can give me your email address and I will email you the link.
There is also a PHP conversion of this on github called php-ews-master
So far we are leaving the signage part out of it, just getting the data to display on a website.
So far we are only working on getting the pressence data from exchange and integrate that in our Asterisk IPPBX system.