Initials in Spanish

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:

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. 

Before Christ and After Christ

In Spanish, the abbreviations for "before Christ" and "after Christ" differ slightly from the English versions. 

Before Christ
Spanish Abbreviation: a. C. (antes de Cristo)
In Spanish, antes de Cristo is abbreviated as a. C., with a period after the "a" and the "C" capitalized. This indicates dates before the birth of Christ.
English Abbreviation: B.C. (Before Christ)
In English, Before Christ is abbreviated as B.C., with both letters capitalized and periods after each letter.

After Christ

Spanish Abbreviation: d. C. (después de Cristo)
The abbreviation for después de Cristo in Spanish is d. C., where "d" stands for después (after) and "C" stands for Cristo. Like a. C., this abbreviation includes a period after the first initial.
English Abbreviation: A.D. (Anno Domini)
In English, Anno Domini (Latin for "In the Year of Our Lord") is abbreviated as A.D., with both letters capitalized and periods after each. 

Note that there are other ways to abbreviate a. C. and d. C. in Spanish; for example, these are also used and correct:

antes de Cristo:

a. de J. C.

a. de C.

a. J. C. 

después de Cristo:

d. de J. C.

d. de C.

d. J. C.

Doubling Letters

Spanish often doubles initials for plural abbreviations which English doesn't.

Some examples are:

EE. UU. = Estados Unidos (USA, U.S.)

The abbreviation is pluralized in Spanish, so each word (Estados and Unidos) is doubled, indicated by "EE. UU." with periods following each letter.

CC. OO. = Comisiones Obreras

In English, "Workers' Commissions" does not have a standard abbreviation, but CCOO is recognized internationally for the Spanish union, with no spaces or periods.

JJ. OO. = Juegos Olímpicos (Olympic Games - OG)

In English, OG (Olympic Games) is used occasionally, but more commonly, people simply refer to them as the Olympics. The abbreviation OG does not follow the Spanish plural convention and uses only one initial per word without periods.

Exception:

Bs. As. = Buenos Aires (BA)

The abbreviation in Spainish uses the first two letters of each word, adding s and separated by a period, forming Bs. As.
In English, abbreviations for Buenos Aires are less formal and often simplified to BA, omitting periods and only using initials.