I can't offer much in the way of the actual regulations, except that they are only sporadically enforced and that there is much complaining. I've been in Medford for 7 years and have had one ticket for parking on a street where you need to buy a pass. Usually tickets appear when neighbors complain.

The group to join in Medford is the medfordmass Yahoo group: http://groups.yahoo.com/group/medfordmass/. It takes 24-48 hours for them to accept you, last I checked. If you post your question there, you might get an answer. It is an active group.