This is the Arabic letter for "N".
You may have seen several people and organisations change their profile pictures on social media to it - including the Church of England and the Archbishop of Canterbury.
You might also have seen people drawing it on their hands.
And using the hashtag #weareN
Share solidarity of prayer and love with victims of terrible suffering in Iraq, especially threatened Christians of Mosul. #WeAreN— Justin Welby (@JustinWelby) July 23, 2014
It is part of a campaign in solidarity with persecuted Christians in Iraq.
Several have had the letter ن put on their doorways, to show that those inside are Nazarene, which means Christians in Arabic.
Christians have lived in Mosul, Iraq's second city, for 2,000 years.
But last month they were told to flee, pay a tax, or convert to Islam by fighters from the Islamic State (formerly known as ISIS). Patriarch Louis Sako told AFP: "For the first time in the history of Iraq, Mosul is now empty of Christians."