First, and foremost, you should try to avoid using abbreviations, acronyms and initialisms whenever possible - try to fill those 3-letter spots with real words. but if you can't find a word that will work, you shouldn't use an abbreviation that you're not familiar with, because that means a lot of people of your age and background will not have heard of it either. SDS is pure crosswordese, these days, in my humble opinion (and I knew people who were in it when I was in college, but that was six decades ago), so I'm pretty sure anyone under 50 has never heard of it except in history books (not likely) or crossword puzzles.