If you look on ebay at any given time, you will usually find a couple listings for "Gregg" pens. This dealer says it's a Sheaffer subbrand, that one says Eversharp, another says Esterbrook . . . so whose brand were these?
The answer is actually none of the above. "Gregg" wasn't the name of the brand, but for the method of writing for which the pen was intended. Gregg Shorthand was a system of stenography invented by John Robert Gregg in the late 1800s and was widely used by secretaries to take dictation in the days before tape and digital voice recorders made the practice obsolete. A great article on Gregg Shorthand, including a complete transcription of the 1929 manual, can be found here.
Gregg writing instruments of the late 20s and 30s usually have the word in a circle comprising two ellipses (I believe that the two ellipses are shorthand for the word "shorthand"). The logo must have been trademarked by Gregg and licensed to various pen manufacturers.
A pen that dared call itself Gregg-friendly boasted of its superior ink flow, able to keep up with the fastest transcription without skipping. That doesn't make much sense in a pencil, since any pencil will write just as fast as you can move your hand. Nevertheless, whether to produce pen and pencil sets or for whatever reason, "Gregg" pencils do exist.
(click on pictures to enlarge)