TITLE: Uppercase Point Labels in High-School Diagrams: from Euclid?
QUESTION [17 upvotes]: I wonder if the convention of labeling points in geometric
diagrams with uppercase symbols ultimately derives from 
Greek mathematics, which was originally written in
"majuscule" (uppercase) Greek script (in contrast to the "minuscule"
script that was introduced much later (9th century?)).
Certainly Euclid and Archimedes used only uppercase,
and all of Descartes diagrams in La Geometrie (1637)
follow the same convention.
It seems that middle- and high-school textbooks continue
to use uppercase labels (is this only in the U.S.?), 
but college texts do not follow
this as rigidly.  This was brought home to me when I wrote
a chapter for high-school teachers and the editors changed
all my lowercase vertex labels to uppercase.
I much prefer lowercase for point labels, although
I do not quite know why I have this preference.
(Maybe because uppercase seems like SHOUTING?)
But when writing for an audience accustomed to
a particular convention, it seems prudent to follow that convention.
My questions are: 
(1) Is the Greek majuscule script the origin of the uppercase
diagram-labeling convention?
(2) In so far as I am correct that the uppercase convention
is followed up to high school but dissolves at more advanced
levels, why does it persist to one level but dissolve beyond?

REPLY [4 votes]: As mentioned by the OP in the comments, Reviel Netz is an academic who thinks about these kinds of questions.  For example, he has a great chapter in "The Archimedes Codex" (by Netz and his coauthor William Noel) on the topic of how the Greeks labelled their figures.  He explains how the philological method - comparing and contrasting different manuscripts to reconstruct a common origin manuscript - can be applied to the various figures in the extant codices of the Archimedean tradition.  He applies the philological method to construct what the figures drawn on the beaches of Syracuse in the third century BCE might have looked like.
However, Netz also notes the innovations of the medieval scribes.  He states (p. 111):

Medieval scribes, at this point, took some crucial steps in the invention of more effective typesetting interfaces.  The use of several cases - an uppercase alongside a lower case - is of great value.  It allows us to separate the letters referring to the diagram (which remains in upper case) from the rest (which is now in lower case).

Thus, Netz appears to argue that the real innovation is not so much writing in majuscule for the figures, but in writing a mix of majuscule and miniscule at the same time.  As pointed out by others, this is a medieval construct.  
(Netz states in passing that the ancient Chinese used different colors to identify the components of their figures.)