It's actually a very rare mis-print, one of a limited line. I've only seen a handful in my life. It should say "SAS" but there was a transcription error at the embroidery plant, which led to the bottom right bar of the "A" being missed off. So it's doubly rare - a limited edition Special Forces TRF, but with additional rarity value for the misprint. I've seen guys fight over them in Hereford, such is the cachet attached to this badge.
Should fetch the owner a tidy sum on eBay - at least £1000 to a Special Forces badge collector.