In cryptography, a Caesar cipher, also known as Caesar's cipher, the shift cipher, Caesar's code or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a left shift of 3, D would be replaced by A, E would become B, and so on. The method is named after Julius Caesar, who used it in his private correspondence.
The encryption step performed by a Caesar cipher is often incorporated as part of more complex schemes, such as the Vigenère cipher, and still has modern application in the ROT13 system. As with all single-alphabet substitution ciphers, the Caesar cipher is easily broken and in modern practice offers essentially no communication security. Source
2. Dancing Man
"The Adventure of the Dancing Men", one of the 56 Sherlock Holmes short stories written by British author Sir Arthur Conan Doyle, is one of 13 stories in the cycle collected as The Return of Sherlock Holmes. Doyle ranked "The Adventure of the Dancing Men" third in his list of his twelve favorite Holmes stories. This is one of only two Sherlock Holmes short stories where Holmes' client dies after seeking his help. The other is "The Five Orange Pips", part of The Adventures of Sherlock Holmes. Source
3. Binary Code
A binary code represents text, computer processor instructions, or other data using any two-symbol system, but often the binary number system 0 and 1. The binary code assigns a pattern of binary digits to each character, instruction, etc. For example, a binary string of eight bits can represent any of 256 possible values and can therefore represent a variety of different items.
In computing and telecommunications, binary codes are used for various methods of encoding data, such as character strings, into bit strings. Those methods may use fixed-width or variable-width strings. In a fixed-width binary code, each letter, digit, or other character is represented by a bit string of the same length; that bit string, interpreted as a binary number, is usually displayed in code tables in octal, decimal or hexadecimal notation. There are many character sets and many character encodings for them.
A bit string, interpreted as a binary number, can be translated into a decimal number. For example, the lower case a, if represented by the bit string 01100001 (as it is in the standard ASCII code), can also be represented as the decimal number 97. Source
4. Morse Code
Morse code is a method of transmitting text information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment. It is named for Samuel F. B. Morse, an inventor of the telegraph. The International Morse Code encodes the ISO basic Latin alphabet, some extra Latin letters, the Arabic numerals and a small set of punctuation and procedural signals as standardized sequences of short and long signals called "dots" and "dashes", or "dits" and "dahs", as in amateur radio practice. Because many non-English natural languages use more than the 26 Roman letters, extensions to the Morse alphabet exist for those languages.
Each Morse code symbol represents either a text character (letter or numeral) or a prosign and is represented by a unique sequence of dots and dashes. The dot duration is the basic unit of time measurement in code transmission. The duration of a dash is three times the duration of a dot. Each dot or dash is followed by a short silence, equal to the dot duration. The letters of a word are separated by a space equal to three dots (one dash), and the words are separated by a space equal to seven dots.To increase the speed of the communication, the code was designed so that the length of each character in Morse is approximately inverse to its frequency of occurrence in English. Thus the most common letter in English, the letter "E", has the shortest code, a single dot. Source
The Matoran Alphabet was the system of written language used mainly by Matoran and several other inhabitants of the Bionicle universe. It is similar in most respects to our own, using a system of circles, dots, and lines to convey the characters in the Latin alphabet.
On Voya Nui and Mahri Nui (most likely because they were once connected) hexagons were used in place of circles and the letter K was slightly modified and resembled the latin letter more than the other version. However, it is unknown if this is merely a cosmetic change, or practical.
Matoran had their own numerals as well. Each of them have a central circle with line segments jutting out of them, but starting with the numeral six, there are two central circles rather than one. Zero has one central circle. Source