"This was done without permission and while we all feel the horror of the recent events, the side of a train is not an appropriate place for this."
Many on Reddit agreed with Hannan, saying that even though it's a nice tribute, people shouldn't vandalise property.
"You don't get to vandalise other people's things just because it's a nice message," one person wrote.
Another agreed: "I don't care how virtuous your intent, you don't graffiti on property that isn't yours without permission."
However, one person believed that the whole purpose of this type of art is that it is intended to be removed.
"The true purpose of graffiti art is that it is transient and created to be destroyed," they said.
"If the artist had intended this to be a permanent tribute, they would have used a different medium."
This is not the first time graffiti has been used as a Christchurch tribute.
Wellington City Council was criticised for removing messages of support for Christchurch terror attack victim but has since apologised, according to RNZ.
Messages saying "Stand together NZ, our people murdered" and "love to all Muslims" were removed by the council's graffiti crews.
The council has since changed their minds and said positive message can say.
Mayor Justin Lester told RNZ the contractors were just doing their job but have advised them to use their discretion.
"If someone's putting up messages that are vandalism or if they're hate messages or contain swearing ... we won't tolerate that, but we will tolerate messages of support being expressed in a positive way," he said.
