A "sigla" is a group of initials that is used as an abbreviation for a word that is part of an entity or a complex name. Some names use a group of initials and they are referred to by these initials in both writing and speaking.
There are certain rules to follow when using "siglas" in Spanish.
Let's see them in detail.
How to read initials in Spanish
Acronyms
Just like in English, the way they read varies. For example, there are initials that are written and read as a single word, i.e. when you say it out loud you pronounce the initials phonetically to form a word. These are acrónimos (acronyms).
Notice that they are pronounced in the same way regular Spanish words are by dividing the sounds by syllable.
For example:
Note that ovni is written in lower case as it has become a common noun in Spanish, also ovni is an example of a word that is an acronym in Spanish, but an initialism in English.
Initialisms
Some initials are difficult or impossible to read, for example if they don't contain vowels; these are read and said pronouncing every initial individually. For example:
UGT stands for Unión General de Trabajadores y trabajadoras.
DGT stands for Dirección General de Tráfico.
It's important to mention that sometimes the way these initialisms are pronounced are the basis for new words, for example we have the nouns:
Some initials use a mixed method when reading them.
For example, the initials for Compact Disc Read Only Memory: CD-ROM are read as [ze-de-rrón] and it actually forms a common noun: un cederrón.
How to make the plural of initials / acronyms in Spanish
Unlike the English, which uses adds -s at the end of initials to mark the plural, in Spanish we do not add -s. Therefore it can sometimes be confusing if it's not clear by the context whether we are referring to the singular or the plural of the word.
Here are some examples in plural:
Gender of initials / acronyms in Spanish
The gender of initials /acronyms is that of the main noun in the full version of what the initials stand for. So, for example, these are masculine:
And these are feminine:
When to use upper or lower case for initials / acronyms in Spanish
Initials / acronyms in Spanish are fully written in capital letters (DNI, DGT, CD, etc) unless they contain more than 4 initials, in which case we only use a capital letter for the first letter, the rest are written in lower case. For example:
If the initials are so widespread that they become a common noun we write it as we would write any other common noun in Spanish, all in lower case (unless it is starting a sentence):
Bear in mind that, as common nouns, they must follow the general rules for written accents.