So, just for funzies, I finally got around to studying and sourcing images for the evolution of the GL insignia itself.
As with the Golden Age (Alan Scott) insignia, the Silver Age Green Lantern symbol would be a stylized representation of the power battery from whence the character drew his power, contained within a circle.
The very first appearance of the symbol was in this Gil Kane panel from SHOWCASE # 22 (1959).
This early symbol was fairly complex, and surely a pain to draw again and again on page after page. Standing in mute testimony to this is the fact that the symbol was in constant flux.
After the new version of Green Lantern was awarded his own ongoing series, the symbol was still in constant flux from issue to issue, and even panel to panel.
At some points, the symbol started to become very simplified and abstract, resembling a simple ring sitting between two bars, but with the domed top of the original power battery design still visible. This gradual simplifying of the design clearly allowed Gil Kane and his inkers to waste less time drawing the symbol.
Circa GREEN LANTERN Vol. 2 # 8, we finally started to see the iconic version of the symbol...but only in the occasional panel or two.
More often during this early period, the symbol tended to be depicted as a very thin ring with two distinctly-separate bars on top and bottom.
Finally, circa GREEN LANTERN Vol. 2 # 13, the iconic version of the symbol became a mainstay...
...but not always, as the “separate sidebars” version would often pop up in random panels and on covers.
During this period, Gil Kane would also occasionally draw the (ever-changing) symbol as a decorative visual accent for captions and/or panel-to-panel transitions, And, in one instance, as a ring-generated mutual greeting between Hal Jordan and Alan Scott, the Golden Age Green Lantern.
It should also be noted that modern reprints of these early stories recolor the symbol to leave the center circle white (as it is in all modern comics and licensed products). In reality, the original printings of these stories consistently colored the entire symbol green...
...right up through Gil Kane’s final regular issue, # 75.
Beginning with (the now-retitled) GREEN LANTERN/GREEN ARROW # 76, the incomparable Neal Adams took over the art chores, and quite consistently stuck with the “separate sidebars” design...
...although, toward the end of his run, he began to experiment with curving the sidebars so that they matched the shape of the circle that the symbol was set within. Judging by the variations seen in Adams’ later comic/commission/sketch art, this seems to be his preferred style.
After the cancellation and relaunch of GL/GA, Mike Grell took over as artist, and it was at this point that the iconic symbol reasserted itself, but was now also colored (inconsistently, of course, though mostly just on covers) with a white central circle. The “separate sidebars” design would also continue to make occasional appearances, depending on the artist and the issue.
Joe Staton would also occasionally give the symbol a little bit of a vertical joint between the central ring and the sidebars...
...but, by this point, the iconic version of the symbol had finally become locked down pretty firmly.
In 1982, the official DC Comics Style Guide would provide the official symbol used for the vast bulk of merchandising and whatnot over the next few decades...
...but this variant with taller sidebars would often also be used for licensing and UPC boxes on covers, and seemed to be the one artists were most often referencing in their artwork. I’m still not sure if this version was designed before or after the Style Guide version, or when/where it first appeared.
As a general rule of thumb, the sidebars are usually the same width as the central ring, and, personally, I find the versions with those particular proportions to be the most aesthetically-pleasing. The Style Guide symbol has sidebars which are thinner than the central ring, which looks a bit “off”.
Of course, the Kyle Rayner era (beginning in 1994) gave us his unique Yin/Yang-style symbol...
...and then there would be other variants across different media (such as John Stewart’s symbol from the JUSTICE LEAGUE cartoons, which was basically a monotone-green version of Rayner’s). Eventually, the post-GREEN LANTERN: REBIRTH (2004) era gave us the modern version of the symbol as we see it today, with the tips of the (now-slanted) sidebars blending into the circle surrounding the symbol.