Hello. Piotr.
            Thank you very much for your answer and links.
There seems to be a vague symbolism of the kind you describe in the Roman alphabet, and little wonder, since if characters are somewhat mnemonic (say, a round shape for a rounded vowel) they are easier to learn; also, in the course of history new letters have sometimes arisen as variants of already existing ones corresponding to phonetically similar sounds, e.g. <U>, <V>, <W>, or <I>, <J> in the Roman script, or omikron and omega in Greek. Latin originally had the same letter <C> for [k] and [g], and <G> was introduced as a modification of <C> by Emperor Claudius. But generally the phonetic value of a letter is not predictable from its shape -- note the characteristic differences between the Roman script and closely related writing systems (Greek, Etruscan, Cyrillic) or very different phonetic values of the same character or combination of characters in various languages using the same script.
Great that you see some symbolism.
I don't pretend graphic symbolism to be universal, I mean there could be several systems
as it happens with phonems, words and sintax. I would like to know if for languages that
have been using an alfabet for a long enough period of time can can be recognized
symbolic traits on theirs graphs be them phonetic, phonemic, syllabic or a mix.
Also, the symbolism i'm speaking about from my point of view is more clear for some
lower-case handwrited alfabets than for capitals. The point would be a psychological
unconscious motivation guiding the evolutions of handwriting.
In Spanish we had the <x> letter for a fricative sound, but there was a reform
of the alfabet as proposed by Andrés Bello and done in Chile, afterwards that
reform failed, but from it came the change of <x> for <j> for the fricative sound,
curiosly the new letter enters better in the paradigm of representing fricative
sounds -as seems to happen with <f> <s> and <z>- by ondulatory or zig-zag traits
of the strokes.
Particularly the <c> and also <v> would be exceptions (to the treats i suggested
where for interrupts and fricative) but these two letters are ambiguous in their
readings, what, then, reinforces rather than weaken the hypothesis of graphic
A consistent phonetic alphabet showing in an iconic fashion the articulatory features of sounds was invented in the mid 19th century (ca. 1867) by the Scottish teacher Alexander Melville Bell, father of Alexander Graham Bell (the same who emigrated to America, invented the telephone and established the Bell Telephone Company, now AT&T). It was called Bell's Visible Speech, and had its ardent enthusiasts, including some British phoneticians of the time and George Bernard Shaw, who mentions it in "Pygmalion":
HIGGINS [to Pickering]. ... I'll shew you how I make records. We'll set her talking; and I'll take it down first in Bell's Visible Speech; then in broad Romic; and then we'll get her on the phonograph ...
The character of Higgins owes much to the great phonetician Henry Sweet, who modified BVS to create the even more scientific Organic Speech system.
I think that Bell's idea of visible speech is quite near of that of king Sejong,
for hang-gul, in 1443 as it relies on a symbolic representation of articulatory traits.

For example, from the second link you gave:

«The fundamental consonant symbol chosen by Mr. Bell is a curve,
open on one side, a C. This typifies an obstruction to the free pas-
sage of the breath, effected, within the oral cavity, by the approximation
of the mouth organs, of tongue and palate, or of lip and lip. In the
position of a C, it signifies an approach of the back part of the tongue
to the soft palate, such as produces the German sound of c/i in ac/i;
turned over, with the curve up, a like approach of a point on the for-
ward surface of the tongue (Mr. Bell gives it the technical name of
front) to the neighboring hard palate, producing the German c/i
sound in ic/i; with the curve turned under, the near application of the
point of the tongue behind the teeth; with the curve to the right, the ap-
proach of lip to lip. If the opening of the curve is closed by a straight
line drawn across its ends, complete closure of the organs, forming a
surd mute, is intimated; in the C-position, a k; in the Q - position,
a t; in the a-position, a p.»

But <c> is actualy an ambiguous graph (as your have pointed it had
the /k/ and /g/ sounds in latin, and has the /k/ and /q/ sounds in
Spanish) and being without vertical strokes (that <k> has), and not showing
zig-zag (as <z> does) but being round as (are <e> or <o>) i think it would

be better suited for symbolizing a vowel sound
than for a consonant.
any case I wouldn't suggest to change it, except if someone happened
to suggest
changing it to another system. 
I don't know exactly wich phonemic or phonetic or articulatory or
may be overall perception trait should be related to the kind of graphic
symbolism of the letters i am speaking about. Let's explain that i was
trying to think of a system as the one of Bell but representing the aspects
of sounds that are seen on the spectrograms and then giving them a more

natural (cursive) shape when i realized that the alfabet itsefl had that features

I've found some useful online information relevant to you query.
Yes. Thank you.
Santander - Cantabria