member, members
Generally lowercase.
Reference to National Geographic members has specific meaning:
National Geographic subscribing member: refers to paid subscribers
National Geographic Society contributing member: refers to a donor
Avoid using “National Geographic member” in other contexts. Someone affiliated with National Geographic can be identified as a fan, viewer, reader, customer, photographer, or user. For example, write: Your Shot user or Your Shot photographer.
Other uses:
member of Congress
member of the Senate
member families
member of the House
member of Parliament
fellow members