Is this something that exists and could be plausible?
Yes, things like that already exist and have even been used by well-known serial killers!
(So much for creating a dramatic intro – lol)
Monoalphabetic Substitution Cipher
What you are referring to, could be categorized as a classical “pigpen cipher”; a monoalphabetic substitution cipher where graphical symbols are used. You might change the symbols and maybe even the way you encode things, but replacing text with symbols will always boild down to a simple, monoalphabetic substitution cipher.
Nowadays, you won´t find too many examples of it in action, but things looked different hundreds of years ago when a simple substitution cipher was able to baffle the masses. Yet, those days have long gone and suchs ciphers can now mostly be found in children's books on ciphers or “secret writing” gimicks packed in breakfast cereal boxes.
The rare exceptions to this rule are limited to things like (for example) the notes from the “Zodiac Killer”. But – all in all – the enigmatic charisma of “danger” and “death” provided more mystery to those notes than the usage of symbols… something which can be broken/deciphered rather easily, assuming enough data or information is available.
Modern Cryptography and Kerckhoffs' Principles
For better understanding: in modern times (and on this site), we tend to handle cryptography according to well-vetted rules… among them some which go back to Kerckhoffs' principles, which defines that a cipher algorithm should be made public (aka: regarded to be known by “the enemy”).
One of the reasons why some notes by the Zodiac Killer haven´t been deciphered yet, lies exactly in that area: the algorithm was never published and the data provided by the Zodiac killer did not provide enough information to deduct the actual contents of the ciphertext with absolute confidence.
Now, please don´t get me wrong. As someone who has professionally designed some fonts for advertising and other purposes, I am always intrigued by the idea of putting some visuals in communication. But I can´t help to share my two cents to spare you from walking the wrong path unwillingly:
Would it make sense from a modern-day cryptographical point of view to create such fonts?
No. Not if you actually expect them to provide any kind of real cryptographic security.
Would it be a nice hobby and find some fans nevertheless?
Sure… as long as you keep in mind you´ll most probably be spending more time creating the fonts than others (cryptanalysts, as well as “ye average” puzzle freaks) will need to break the ciphertexts created with them.
Let´s take your font idea and put it on the front page of a newspaper as you implied. That might work once. But the more you publish, the more data will be available and since we´re practically talking about a monoalphabetic substitution cipher, it won´t take too long for the first people to decipher your stuff by “guessing” the keys (with merely a sprinkle of Cryptanalysis).
Especially, since you´re even limiting the security down to…
… instead of the 256 “peaks” (= 8 bits = 1 unsigned byte) we work with in modern crypto.
As a simple rule of thumb: The smaller the alphabet, the easier the cryptanalysis!
I surely agree with you that one can hide a secret in the open. But as soon as someone knows there´s a secret to look for, security starts to fade towards zero. That´s where you need a secure cipher, and – whether we like it or not – fonts can not replace cryptographically secure algorithms.
If you want to take a look around at the different fonts and symbols, use your preferred search engine to check on “cryptography symbols“ and co.
You´ll also discover your idea is already used and published in newspapers as (cryptographic) puzzles. There are even a few pages diving into such graphical ciphers. One of many: http://www.phantomgallery.64g.ru/shiphen/cod6en.htm