Morse code prosigns or procedural signals are dot/dash sequence symbols that are not intended to represent written characters, but instead are used to manage transmission and formatting of messages. Many prosign symbols have been in use in their present forms since the 1860s.
Prosigns are symbols that have specific functions, such as indicating changes of transmission communications protocol status, indicating textual white space, and text formatting. Morse prosigns play a role similar to the role played by the nonprinting control characters of teleprinter and computer character set codes such as Baudot or ASCII.
In the early decades of telegraphy many operating efficiency improvements were incorporated into telegraph operations, including the introduction of Morse symbols known as procedure signs or prosigns. Prosigns were not defined by the inventors of Morse code, but were gradually introduced over time, and greatly improved the speed and performance of daily high-volume message handling operations.
Improvements to the legibility of formal written telegraph messages (telegrams) by means of white space formatting were thus supported by the creation of the additional new procedure symbols. Mastery of these special Morse code prosigns is an important part of becoming a fluent and efficient telegrapher/telegraphist.
Prosigns may be represented in printed material either by a sequence of dots and dashes, or by a sequence of letters, which, if sent without the normal inter-character spacing (concatenated), correspond to the prosign symbol.
For example, when embedded in text the Morse code dot/dash sequence (▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄) represents the character "=" or "—"; when it appears alone it indicates the action of spacing down two lines on a page in order to create the white space indicating the start of a new paragraph or new section in a message heading. There is no actual written or printed character representation or symbol for a new paragraph (no symbol corresponding to "¶"), other than the two line white spaces themselves. Many Morse code prosigns do not have written or printed textual character representations in the original source information.
Of methods used to represent Morse prosign symbols there are at least three:
Some prosigns are in use for special characters in languages other than English, for example "Ä" and AA, neither of which is part of the international standard. Other prosigns are officially designated for both letters and prosigns, such as "+" and AR.. Some genuinely have only one use, such as CT or KA (▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄), the International Morse prosign that marks the start of a new transmission or new message.
|Prosign||Code Symbol||Meaning||Comments||Memory Aid||Verbalization||As text|
|AA||▄▄▄▄▄▄▄▄▄▄▄▄▄▄||Start new line||Space down one line; typewritten as Carriage Return, Line Feed (CR-LF). Also written RT.||"Add A line"||"didahdidah"||Ä, Á|
|AR||▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄||Message separator, start new message / telegram.||New Page, space down several lines. Decoder software may show "+". Alternative for "Break" in conversational Morse. Also written RN.||"All Rendered" or
|AS||▄▄▄▄▄▄▄▄▄▄▄▄▄▄||Wait ||Respond with: SN, or characters "R" (Received) or "C" (Confirmed).||"Wait A Sec"||"didahdididit"||&|
|BT||▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄||Start of new section / new paragraph.||Space down two lines; typewritten CR-LF-LF. Decoder software may show "=".||"Begin Two"||"dahdidididah"||=, — |
|CT||▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄||Start of transmission Start of new message.||Attention commencing transmission. Also written KA.||"Copy This"||"dahdidahdidah"|
|HH||▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄||Error / correction||Always followed by correct text. Sometimes transcribed as "????". Sometimes written EEEEEEEE.||"Error"||"didididididididit"|
|K||▄▄▄▄▄▄▄▄▄▄▄▄||Invitation for any station to transmit||Lone alphabetic character "K" at the end of a transmission.||"oKay, go ahead"||"dahdidah"||K|
|?||▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄||Please say again||Lone question mark "?" from the receiving station in response to a transmission.||"huh?"||"dididahdahdidit"||?|
|KN||▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄||Invitation for named station to transmit||Go ahead, specific named station. Decoder software may show "(".||"oKay, Named"||"dahdidahdahdit"||(|
|NJ||▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄||Shift to Wabun code||Shift from Morse code to Wabun code Kana characters. Also written XM.||"Next Japanese"||"dahdididahdahdah"|
|SK||▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄||End of contact / End of work||Also written VA.||"Silent Key"||"didididahdidah"|
|SN||▄▄▄▄▄▄▄▄▄▄▄▄▄▄||Understood. Verified.||Message received and checks okay. Alternatively shift from Wabun to Morse code. "SN?" verification requested. Also written VE.||"Sho' 'Nuff" or "VErified"||"didididahdit"||Š, Ś|
|SOS||▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄||Start of distress signal||Only used by original message sender, and only for imminent danger to life or property. ( listen (help·info))||"Save Our Souls"||"didididahdahdahdididit"|
|BK||▄▄▄▄▄▄▄▄▄▄▄▄ ▄▄▄▄▄▄▄▄▄▄▄▄||Break in conversation||Morse abbreviation for "back-to you". In conversational Morse some use AR, KN, or "K" instead.||"BreaK"||"dahdididitdadidah"||BK|
|CL||▄▄▄▄▄▄▄▄▄▄▄▄▄▄ ▄▄▄▄▄▄▄▄▄▄▄▄||Closing down||Abbreviation for "closing station" (Morse abbreviation).||"CLosing"||"dahdidahditdidadidit"||CL|
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