As a Jamaican, I can tell you that if we say 'one love' it can mean 'bye', 'peace' etc. I think it became popular through Bob Marley's song 'One love'. 'One love' when used in sports means that the score was 1-0. So the team that lost (got '0') got 'one love'

it comes from american hip-hop taste. as Alipetgis mentioned, we say that end of the convasation. `peace out` `one love peace` `one love` etc,. it is bye, also sharing our mind. sharing we have same mind or taste. but it is not for everybody, somebody `share` same flavor. MV by Nas `One Love` http://jp.youtube.com/watch?v=hrngXKmJXAY&feature=related this will give you the flavor :D