The upper charge is in fact a circular 'E'. Thus the upper and lower charges represent EC - Explorers Club. The central charge might in fact represent a compass rose - very appropriate for an exploration society.
According to its website, the Explorers Club was founded in 1904-05 by survivors of F.A. Cook's 1894 Arctic expedition aboard the Miranda. The club lends numbered copies of the club flag to its members to fly on non-commercial expeditions or field research intended to collect scientific data on remote areas of the world. The members must return the flags to the club upon conclusion of the expedition. The website has several years' accounts of these "flag expeditions." The picture of the flag is in several locations on the site
The flag is a registered trademark of the Explorers Club. Another version with yellow field, letters, and symbols, and a black diagonal band can be found on the site of the Golden Gate (San Francisco) chapter of the club and is apparently that chapter's flag.
Note the very important part the flag plays in this group. The 'official' expeditions by members carrying a flag are called "Flag Expeditions", and when they return, they are required to place a scientific "Flag Report" on file with the society.
The Explorers Club website reports its "flag represents an impressive history of courage and accomplishment and has been carried on hundreds of expeditions by Club members since 1918. To carry the Club flag is an honor and a privilege. It has flown at both poles, from the highest peaks of the greatest mountain ranges, traveled to the depths of the ocean, to the lunar surface, and outer space. A flag expedition must further the cause of exploration and field science.
The flag was designed by Frederick S. Dellenbaugh, one of the Club's founding members. Between the red of "courage" and the blue of "fidelity" lies a broad white diagonal displaying the initials of the Club's name and a compass rose, symbolizing the worldwide circle of the Club's interests. Over time, each of the two hundred and two numbered flags develops a unique history."
What are the correct shades of The Explorers Club flag? Judging by the Club's web site, Joe McMillan's rendition possibly uses too dark a blue; I suspect the Union Jack's blue (RGB 0, 35, 119) and red (RGB 193, 18, 31) should be used instead.
I have no special information on the shades used by the club itself. My image is in the nearest FOTW-standard approximations to the colors Daniel cites, RGB 0:0:102 (B+++) and 204:0:0 (R+). It is probably more likely that US flag-makers would use Old Glory red and Old Glory blue (the government specified shades for the US flag) than UJ red and blue, but in any case I believe discussions on the list have concluded that B+++ and R+ are the right BS colors for both the S&S and the UJ.