Here’s a place to collect gifs of the Fi – Snarling Smile signal, which is described thusly: “The smile rises towards the nose, while forming an H pattern of mouth tension from the levator and depressor muscles contracting up and down together."
The gifs don’t need to show just this one signal in isolation, necessarily – as long as the relevant signal is clear.
Here’s two examples of Allison Raskin, who is in the database as NeFi l—, exhibiting a snarling smile.