I'd use whatever abbreviation SAFe gives you (usually certification bodies mention the preferred abbreviation when you get your certificate) In regards to job postings, I've only seen a few that want a SAFe certification and they don't specify which one - although that may vary.
Also, I really recommend that for any certification you spell it out on a resume and follow it with the abbreviation. ie) Project Managment Professional (PMP) etc.
There's definitely some certifications that are a little more obscure that not a lot of people/recruiters are aware of. I have a certification in clinical research (I work in the pharma industry) and outside of some segments of pharma no one knows what this certification is. Saving Changes...
Jared PadgettVerizon MediaVentura, Ca, United States
The SAFe abbreviation is on the certification itself. For a SAFe 5 Certified Agilist, the abbreviation is SA.