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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