Yeah, never heard of it myself. Google searches yields nothing.
The rubbery matte finish has gotten sticky over the years and colors off on your hands. Typical of many cameras og the 90's. Sigma described it as "ZEN Matte finished to provide a non-slip, non-reflection and scratch resistant body, which is sturdy and serviceable through many years" - so I guess not meant to last for ever...
I have learned from someone on these forums that the sticky finish will come off with (medical) adhesive remover, leaving the body surface smooth and glossy. I will give it a try but it will probably also remove all the labelling so gotta take some photos to remind me of the
buttons functions.