Do you really not see the difference between these abbreviations?Do a search on this forum for "SB" which of course stands for ScubaBoard, and for DM which means divemaster. Are all these members who have capitalized the term, also simply and irrefutably wrong? Is Miriam Webster (click here) wrong when they give examples of capitalized abbreviations for single words as part of the definition of acronym? See the part about "compound term" in the first paragraph if you're confused.
1. Facebook -> FB
2. decompression -> deco
#2 cuts off letters ONLY from the end of the word, and keeps part of the word intact. It is pronounced as written. This is similar to using a word like "ad" for "advertisement". Or do you also write AD in all-caps – "I'm running an AD campaign for my company" – making it look like the more common acronym (Anno Domini)?
#1 is pronounced by saying the individual letters "Eff Bee", although it's mostly used in writing, and the word is even a compound word created by putting "face" and "book" together, so it works almost like a normal acronym like "FBI" for "Federal Bureau of Investigation"
Let's use Instagram as an example. Common abbreviations are "IG", "Insta" and "gram". Would you put "INSTA" and "GRAM" in all-caps?
ETA:
You know if you keep writing DECO, people might think you are using an actual acronym and try to spell it out. Do you want people to think you are: Dumb Entity Clearly Obtuse?