ANSWER: When should you use periods in abbreviations?

[lady-ganesh.livejournal.com]

Is it just a fanfic thing to drop the periods in the abbreviations or has it become “acceptable” outside of fanfic as well? (ex. NCIS vs. N.C.I.S., SGC vs. S.G.C.)

While fanfic has been around for a long time, so have dropped periods in abbreviations. In fact, if you go to the Official NCIS website, you'll notice even the United States government drops the periods.

Unfortunately, whether or not the dropping is "acceptable" depends on who you're writing for and what style you're using.

( Dropping periods in abbreviations, and also some notes about style and consistency )