This means a big smile, the “:” is the eyes, “D” is the laughing mouth. Ps: Are you worrying about your hot-spot signal? You can try WiFi Booster! Get it now for free on Google Play Store. Download: https://goo.gl/wspPkP. read more
If it is, it's an Easter egg hidden at Google Chrome on Android devices when you opened over 100 tabs. For incognito mode, the icon appeared as “;)”. read more