Shift Out and Shift In (SI) are ASCII

ASCII

The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...

 control character

Control character

In computing and telecommunication, a control character or non-printing character is a code point in a character set, that does not in itself represent a written symbol.It is in-band signaling in the context of character encoding....

s 14 and 15, respectively (0xE and 0xF).  The original meaning of those characters was to switch to a different character set and back.  This was used, for instance, in the Russian

Russian language

Russian is a Slavic language used primarily in Russia, Belarus, Uzbekistan, Kazakhstan, Tajikistan and Kyrgyzstan. It is an unofficial but widely spoken language in Ukraine, Moldova, Latvia, Turkmenistan and Estonia and, to a lesser extent, the other countries that were once constituent republics...

 character set known as KOI7

KOI7

KOI7 is a 7-bit character encoding, designed to cover Russian, which uses the Cyrillic alphabet.In Russian, KOI7 stands for Kod Obmena Informatsiey, 7 bit which means "Code for Information Exchange, 7 bit"....

, where SO starts printing Russian letters

Russian alphabet

The Russian alphabet is a form of the Cyrillic script, developed in the First Bulgarian Empire during the 10th century AD at the Preslav Literary School...

, and SI starts printing Latin letters

Latin alphabet

The Latin alphabet, also called the Roman alphabet, is the most recognized alphabet used in the world today. It evolved from a western variety of the Greek alphabet called the Cumaean alphabet, which was adopted and modified by the Etruscans who ruled early Rome...

 again. SO/SI control characters also are used to display VT-100 pseudographics, and emoji

Emoji

is the Japanese term for the picture characters or emoticons used in Japanese electronic messages and webpages. Originally meaning pictograph, the word literally means e "picture" + moji "letter". The characters are used much like emoticons elsewhere, but a wider range is provided, and the icons...

 (Japanese picture icons) on SoftBank Mobile. ISO/IEC 2022

ISO/IEC 2022

ISO/IEC 2022 Information technology—Character code structure and extension techniques, is an ISO standard specifying...

 standard specifies their generalized usage.

Some older printers

Computer printer

In computing, a printer is a peripheral which produces a text or graphics of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most new printers, a...

 used these characters to control special features, such as changing the font

Font

In typography, a font is traditionally defined as a quantity of sorts composing a complete character set of a single size and style of a particular typeface...

 or ink color

Color

Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...

. On the Teletype

Teletype Corporation

The Teletype Corporation, a part of American Telephone and Telegraph Company's Western Electric manufacturing arm since 1930, came into being in 1928 when the Morkrum-Kleinschmidt Company changed its name to the name of its trademark equipment...

Model 38, SO switched to red printing while SI switched back to black printing.