Thirlwall is nothing but loyal to her band! She commemorated a decade of Little Mix with a tattoo on the back of her calf. In a mysterious code, the tattoo spells out the date of 19 Aug., 2011 — the exact day Thirlwall was put together in a group with Pinnock, Edwards, and Jesy Nelson to form the global phenomenon that was Little Mix.
Besides that tattoo, and on the same foot as the friendship heart, Thirlwall has an inverted triangle. She hasn't spoken about what this means, but she got it in November 2019.