Actor Mark Wahlberg and his wife Rhea Durham posed for a photo together with a mysterious black mark on their foreheads. Do you know what it means?

Wahlberg posted the photos on Facebook and Instagram with the caption: "Wishing all who celebrate a blessed #AshWednesday."

Ash Wednesday is observed by practicing Catholics to begin the 40-day period before Easter. It's a time of prayer, penance, fasting, and good works. On this day, ashes are distributed on foreheads in the form of a cross as a reminder of Jesus' death on the cross.

Here's his Facebook post:

He also posted on Instagram:

Wahlberg, who was raised Catholic, has been very public about his faith. He describes it as "the anchor that supports everything I do in life." He went on to say, "In my daily prayers, I ask for strength, guidance in my vocation as a husband and as a father."

Good for Mark Wahlberg for raising awareness about this little-known custom! Now you'll know what it means when you see someone with ashes on their forehead.