It's usually because the cPanel Analytics is enable in WHM. Please see screenshot on where to find it and where to disable this feature. Even after you disable this feature, the corner smiles will stay for a while. It will go away after a few days or a reboot.
I had not see this corner smile until I enable the cPanel Analytics.
I'd clear your browser cache, removing cookies/sessions, etc and then re-login. cPanel caches everything so it would make sense that it still persists afterwards.
I think Jean is right, however that this icon belongs to cPanel Analytics.