On my car, I have a "Low-Number Reserve Plate" which is very difficult to obtain here in Massachusetts - political connections can secure one, and/or various government jobs - but since 1997, the state RMV holds a lottery so 200 members of the "general public" can vie for one. Low number plates are NOT vanity plates (which must start with two letters), but rather plates that start with numbers or a letter but have less than the six digit norm. My particular plate dates from the 50s, and has been passed down to me from my grandfather. My father has a low digit number as well, highly sough after items here. Both plates are family heirlooms; people find it odd that one could have such an attachment to a set of numbers / letter combinations.
Mine are in "X 9999" series, and "999 X" series - but Reserve Plates can run the gamut from "1" to "99999," mush more impressive than any vanity plate IMO.