"We know that transgender women will continue to be subjected to violence for as long as they are being placed in men's prisons. This is the direct and inevitable result of the Department of Corrections' policies.
"For as long as Sam Lotu-Iiga refuses to take responsibility for these atrocities, there will be blood on his hands," the note concluded.
Passer-bys took a second look as they walked past the office this afternoon, with one man remarking, "What's that going to achieve?".
A spokeswoman for Lotu-Iiga said police were investigating the incident.
A forensic investigator had examined the scene for evidence.
In August, Corrections apologised to Jade Follett, a transgender inmate who faced down threats from inmates in Rimutaka prison before gaining a transfer to a women's prison.
Follett's request to transfer to a women's facility had been delayed when a staff member went on leave.
A policy came into effect earlier this year which gave transgender prisoners who had not formally changed their gender on their birth certificate the option to apply to be placed in a prison which matched their gender identity.