The Sacred Heart of Jesus is a very popular Catholic devotional image and it consists of several symbols.  The Sacred Heart Medal is to remind us of the Passion of Christ on the cross hence the crown of thorns.

The devotional theme for June is the Sacred Heart of Jesus, which is one of the most popular devotions within the Catholic Church.  It began around 1672 when Jesus appeared to St Margaret Mary Alacoque and revealed to her the devotion to His Sacred Heart.