From the Maitland Mercury report:
Maitland City Council announced on Wednesday that the missing plaques weren’t the result of vandalism, as feared by Les Darcy Committee members, but were removed by them earlier this week to allow maintenance on the iconic statue.
Engineers removed the plaques after noticing the base of the statue was separating.
Council projects and building services manager Graeme Matthews said that, ironically, the plaques were removed to prevent their theft.
Full article available at Maitland Mercury, June 7, 2016.