The Guardian style is: > Use all capitals if an abbreviation is pronounced as the individual letters (an initialism): BBC, CEO, US, VAT, etc; if it is an acron

The Guardian style is: > Use all capitals if an abbreviation is pronounced as the individual letters (an initialism): BBC, CEO, US, VAT, etc; if it is an acronym (pronounced as a word) spell out with initial capital, eg Nasa, Nato, Unicef, unless it can be considered to have entered the language as an everyday word, such as awol, laser and, more recently, asbo, pin number and sim card. Note that pdf and plc are lowercase. https://www.theguardian.com/guardian-observer-style-guide-a https://www.theguardian.com/guardian-observer-style-guide-a