Morse code was later made the standard by the International Telecommunication Union (ITU). Morse's original code specification, largely limited to use in the United States and Canada, became known as American Morse code or "railroad code". American Morse code is now seldom used except in historical re-enactments. In aviation, pilots use radio navigation aids. To ensure that the stations the pilots are using are serviceable, the stations transmit a set of identification letters (usually a two-to-five-letter version of the station name) in Morse code. Station identification letters are shown on air navigation charts. For example, the VOR-DME based at Vilo Acuña Airport
Morse code mnemonics the elements of the Morse code characters onto pictures for easy memorization. For instance, "R" () might be represented as a "racecar" seen in a profile view, with the two wheels of the racecar being the dits and the body being the dah. Syllabic mnemonics are based on the principle of associating a word "or" phrase to each Morse code letter, with stressed syllables standing for a dah and unstressed ones for a dit. There is no well-known complete set of syllabic mnemonics for English, but various mnemonics do exist for individual letters. In the Czech language, the mnemonic device