It is ONE frame of the GIF and the middle finger is halfway not there. But it was visible in the “lighting” inside the anvil part of the icon.
Edit: MinecraftForge/forge.gif at 1.7.10 · MinecraftForge/MinecraftForge · GitHub
Seems like they didn’t actually change it, it was mostly the differently configured Gamma from me switching to Linux a few years ago that made it harder to see for me. It is still there.
Edit 2: Okay I just tried to replace it within GT6, but it did not load my Version, so I am certain I cannot change it easily without lots of hacking and potential ASM fuckery.