What are Drug rep pens?

A drug rep pen is a pen given out by Drug companies[the"drug rep"] and given out to doctors and other health care administrators,as a reminder/promotional tool to help sell patented drugs the giants [like MERCK,Wyeth,Phizer,etc.]; are promoting.Many people like to collect these.It can be a challenge to find certain drugs on a given pen,as well as the fact that some pens are rare and so quite valuable.