Where you ever able to get a answear to your question

I am assuming that your firm/company/organization is like most in the America and only has a small WPV policy in a handbook that no one has really read and most likely was "cut and pasted" into the manual from the internet.  Even worse, by your submitted question, it appears your firm has not provided training to employees re. emergency procedures, I am truly sorry.  But alas there is hope.  Our firm, among a couple reputable ones, offers workplace violence prevention training.  In our seminar policies and procedures are discussed at length as well as threat management teams and more importantly this training is customized to your specific firm. 

To answer your specific question, You company needs to have a meeting/training to discuss what you have available for alerting company employees of threats.  Some use a paging system or tone system over PA.  It really depends on the set up of building and type of company, and a few other concerns. 

Hope this gives some ideas.  www.proactiveprotection.net