Why does my phone give me a notification square with a smiley face like this -> :-) <-?

[AC Question]

Just like the one when you're running out of battery, this white square appears with a smiley emoji
I don't understand why, is it a virus? I can provide a screen shot.

 

[Ssaannttii]

My phone does this as well. It could be a virus, even though I ran quite a few antiviruses on my phone and nothing came out wrong...