> Facebook Messenger has the best UX paradigm for this I've seen Viber had a similar thing long before FB's messenger: single gray check mark character if the

> Facebook Messenger has the best UX paradigm for this I've seen Viber had a similar thing long before FB's messenger: single gray check mark character if the message is sent, double gray check mark if it is received by the recipient and double check mark in purple if it is seen. The only issue is with the purple color of the "seen" as it can sometimes blend into an image behind it (if the message was consisting of an image).