Publicly available personal information is particularly tricky; unique identifiers like social insurance numbers or social security numbers are both private and public depending on the context and location. For example, in some countries or counties home ownership records are public, including unique numbers, full legal names alongside addresses. Cities have already struggled with such issues in the debate over open records versus private information; the City of Seattle’s issues have been well documented.
Personally, it’s license plates that have always fascinated me. For a detailed non-privacy discussion and background on plates (or tags as they may be called), turn to our friends at Wikipedia. They are (under every jurisdiction so far) considered to be non-personal information. Designed to be identifiable, in the case of personalization, they’re also an expression of identity. Type of car, color, bumper stickers, etc are subjects of stereotyping for good reason (a non-scientific breakdown of car ads here).