just look in your phone's notifications to find out......but my guess is that this is not your phone. if that is the case, then just ask the person who owns the phone.
we get this question everyday. you see there are millions upon millions of apps out there, each with their own notification icons. unless it is an app like facebook or youtube, most of these questions go unanswered.
hopefully someone else might recognize it.....so i wish you luck, but do not hold your breath for an answer.