Personal ledgible quick cipher The problem:

When I'm writing or reading information (be it on a screen or a physical medium) the information is vulnerable. So long as I'm not alone, anyone can simply glance at my screen or journal and instantly read what's written there (like addresses, phone numbers, and plaintext passwords/device pins)

My goal:

I want to create/utilize some sort of text-obfuscation system or cipher system that makes it impossible for the casual observer (>99.99% of people) to tell what I'm writing or reading at a glance.

The challenges and conditions:


Reading and writing speeds shouldn't be more than 50% slower with practice (I should be able to type this obfuscated text at 50 wpm and read/skim-read at several hundred)
I'm not a math-savant so any obfuscation/encryption operations need to be doable with minimal math and without a computer
From a security standpoint, the obfuscation/encryption doesn't need to be extremely secure, it only needs to be good enough that your average Joe (again, >99.99% of people) could spend several minutes reading over my shoulder without figuring out what I'm reading or writing


Potential solutions I've thought of:


Teach myself an uncommon written language like Esperanto or Klingon which very few people can read
Replace the symbols I use to write letters with alternatives, like Elian-script


My question:

Surely, this is a problem people have grappled with before. Besides operational-security solutions like making sure nobody's looking at your screen or using a polarizing filter, what solutions are out there?
Teach myself an uncommon written language like Esperanto or Klingon which very few people can read


That's not a bad idea. Although if you had to choose one I'd personally advise you to use Klingon instead of Esperanto. The amount of worldwide Esperanto speakers is about 1 in 4000 (0.03%), whereas Klingon is spoken (fluently) by only 20 - 30 people.

The goal of Esperanto (as you might know) was to introduce a universal language with the intent of making the learning process fairly easy, some might even say that Esperanto is very easy to learn. Many words are derived from European languages:


  [...] took most of [...] Esperanto root words from languages of the Italic and Germanic families, principally Italian, French, German,
  Yiddish, and English. A large number are what might be called common
  European international vocabulary, or generic Romance
  
  - Esperanto etymology (Wikipedia)


It's likely that European speakers can recognize some words from Esperanto and maybe in rare instances connect the dots to gain contextual knowledge of a text.

Additionally, there are numerous Klingon &amp; Esperanto online translators (if anybody should get hold of a text).




  Replace the symbols I use to write letters with alternatives, like Elian-script


That's probably a good method. If you do this every day it should be fairly easy for you to learn reading and writing in a cipher and obviously you can invent such a cipher yourself.

However, I have to say that it's unlikely to go beyond a monoalphabetic substituition cipher. Polyalphabetic substituition ciphers are rather hard to do fast by hand / mentally for numerous reasons.