don't recognize it. we get this question on a daily basis here. unfortunately most of these questions go unanswered. there are millions of apps each with their own notification icons. so unless the app in question is like apps like facebook or youtube, most might here might not recognize it.
the easiest way to know is to look on the phone. but for most here, they ask because it is not on their phone. so i would just ask the person what it is. but i guess this question is not as easy to ask as it sounds.
anyways i wish you luck, you might get lucky and someone here might know what it is. but do not hold your breathe for an answer.