Markis’s name day is April 25, the feast of Mark the Evangelist.
Churches that follow the Old (Julian) Calendar keep the same feast on May 8 of the civil calendar. See everything commemorated on April 25.
The saint behind the name

Mark the Evangelist
April 25, Apostle, Μάρκος ο Ευαγγελιστής
St. Mark the Evangelist, one of the Seventy, was a companion of the Apostles Peter and Paul, and wrote the second Gospel, which ancient tradition holds preserves the preaching of Peter. He labored in the spread of the Gospel from Jerusalem to Rome, and is honored as the founder of the Church of Alexandria in Egypt.
Also celebrating on April 25
These names share the feast, many of them other forms of the same name:
What to say on a name day
The Greek wish is Χρόνια Πολλά (Chronia Polla), “many years.” A call or a short message on the day is what people remember. See name day wishes you can send and what a name day is.