Taken from a website:

On March 1st, as a sign of support towards those struggling, we ask as many people as possible to write the word "LOVE" somewhere visible on their arm. March 1st is national self-harm awareness day.

To Write Love on Her Arms is a non-profit movement dedicated to presenting hope and finding help for people struggling with depression, addiction, self-injury and suicide. TWLOHA exists to encourage, inform, inspire and also to invest directly into treatment and recovery.
Link: To Write Love on Her Arms > Home