can't remove picture frame from my box says I have no permission too. and /sili comes up as unknown command when I try to place item pic on my box

sili command works but still can't remove sign

How are you trying to remove the sign?

removertool plugin

You have to remove using the command. Doesn't support remover tool as it's doesn't provide a way to let it know that the entity can be removed. 

ok thank you