Subway is testing a new "Creamy Sriracha Sauce" in at least a few stores in southern California as well as Florida. Sriracha is a Thai hot sauce that's popular in Thai and Vietnamese cuisine where it's most often used as a dipping sauce or as a condiment for Vietnamese pho (beef noodle soup).
However, it's gained popularity and use in recent years in the culinary community. It was even named the "Ingredient of the Year" for 2010 by Bon Appetit. Here's a hilarious comic strip from The Oatmeal regarding the use of Sriracha.
The new sauce was first spotted by Foodbeast out in Santa Ana, CA and was later found by a GrubGrade reader in Florida where it's offered in the Sriracha Chicken Melt. Since Santa Ana isn't terribly far from Los Angeles, I called my local Subway to found out if they had it and walked over to check it out for myself (review to come... when my mouth stops burning), snapping the above photo while I was at it.
Not a big fan of hot sauce but I will be open to trying that.