5. **Who are some of the most prominent collectors or experts in the field of Doctor Who memorabilia, and what contributions have they made to the community?
5. **What factors determine the value of exonumic items in the collectors' market, and how do rarity, condition, and historical significance contribute to an item’s desirability and price?
4. **How have technological advancements impacted exonumia, particularly in terms of production techniques and security measures, and what are some notable examples of these advancements?
3. **What role did transportation tokens play in urban economies and daily life during the 19th and 20th centuries, and how has their relevance transformed with changes in public transit systems?
2. **How do historical events influence the creation and design of exonumia, such as tokens and medals, and what can they tell us about the cultural and social aspects of their times?