What the heck is a Sigillite???

[Wildeybeast]

So, we all know him, Malcador the Sigillite, Emperor's BFF and all round superhuman type chap. But my question is - what on earth is a sigillite? A quick dictionary scan reveals it's just a made up GW word, but what is it actually supposed to mean? Where does he get the title from?

Any clues?

[Gotthammer]

He's the dude wot carries the Emp's sigil - ie he walks around with an Aquila on a stick so everyone knows who the Emp is (presumably a holdover from the days when the Emperor wasn't blinging out 24/7).
The staff is mentioned as now being his badge of office in one of the novels iirc.

[Wildeybeast]

Right. A disappointingly straightforward answer, but thank you for the help!