Every year Christians around the globe enter into a season of repentance called Lent. Often beginning that time is observance of Ash Wednesday. In this observance, ashes are placed on the forehead as a symbol of repentance and sorrow for sins committed.
Ashes, from an early time, have expressed mourning. In Job 42:3–6. Job says to God: "I have heard of thee by the hearing of the ear: but now mine eye seeth thee. The other eye wandereth of its own accord. Wherefore I abhor myself, and repent in dust and ashes." (vv. 5–6, KJV) In the New Testament Jesus went into the desert to fast and pray and this too is incorporated into the understanding of what Ash Wednesday is because Lent is a time of prayer, fasting, self-denial, and focused spiritual growth.
Thus from ancient times, has come the connection of repenting and ashes. During the middle ages, the Christian Church was dealing with a population largely unable to read, and so they developed many rituals and used various visual and auditory means to teach about the faith (banners, carvings, stained glass windows, choirs, etc.).
Today, many churches conduct an Ash Wednesday or a Day of Repentance observance. Palm fronds kept from the previous Palm Sunday are burned and their ashes are used. Alternately, some pass out small cards for people to write down their sins or errors and they are communally burnt and the ashes used. Some even fast for all or part of the day in order to signify the import of the time in the calendar of the Christian faith. Just as night is needed to joyfully welcome a new day, the season of self-denial, interior growth and contemplation of God bring added meaning and power to the celebration of the Risen Lord.
Even if your congregation or church does not conduct such an event, a person can still take part in setting aside the next forty days until Easter (Resurrection Day). In that time intentionally add fasting, prayer, Bible study, services of kindness and mercy. Lent is reflective of that time when the seed is in the ground growing, changing, becoming... Use Lent as a time to begin to grow in your spiritual life, reach out in Christian service and learn and pray more.