348 front plate mount

Prior to 1988, in Massachusetts, the registry only issued drivers a single plate for the rear of the vehicile. These plates can be recognized by the green numbers on them.

After 1988 the law was changed and it required newly registered vehicles to carry plates on both the front and rear. The numbers on these tags were changed to red. If you still have an old registered green numbered tag, like me, you can still use it and it's only required on the rear of the vehicle.

 

CVC 5200:

Display of License Plates

5200. (a) When two license plates are issued by the department for use upon a vehicle, they shall be attached to the vehicle for which they were issued, one in the front and the other in the rear.

(b) When only one license plate is issued for use upon a vehicle, it shall be attached to the rear thereof , unless the license plate is issued for use upon a truck tractor, in which case the license plate shall be displayed in accordance with Section 4850.5.
Amended Sec. 27, Ch. 594, Stats. 2003. Effective January 1, 2004.

Vanity plates can be ordered as one or as a pair. Technically if you ordered a pair, you need to display both. But I think as long as an officer sees it is a vanity plate, they don't bother writing a fix-it ticket. Of course this only applies to custom plates, not sequentially numbered special interest plates. And this is California only (CVC = California Vehicle Code).