How can I visually tell which trucks are > 12k lbs (ie what types of vehicles are > 12k lbs sans freight)?

Although trucks over 12,000 lbs are already prohibited from our neighborhood, semis and large trucks routinely speed through our residential streets. In order to visually quantify the issue, we were wondering if certain cles of vehicles are automatically over 12k lbs (i.e. Are semis always greater than 12k, what about other vehicle types?). I searched the web for these types of weight clifications to no avail. Thanks for your help!