Final answer:
The firearm license should prominently display information about its currency and the capacity of allowable firearms to be readily inspected.
Step-by-step explanation:
The question appears to be focused on the requirements for the display of credentials on a firearm license. More specifically, it asks which details must be clearly visible for inspection on such a license. In the context given, which pertains to the legalities surrounding firearm ownership and the conditions under which police could issue licenses, the important elements that often need to be prominently displayed on a license would include information such as currency (to make sure the license is up-to-date) and capacity (which could refer to the class or type of firearm permissible under the license). Accuracy, safety and security measurements, years of service, and the age of licensee are generally internal considerations or personal qualifications and do not pertain to the license's display requirements. Therefore, currency and capacity are most likely to be the correct answer.