Disabling changing of users avatar and sig

[ctimes]

We have a group which goes through a joining process on my forum and we give them a certain avatar and sig so mods know who is in traning and who isn't (those with their own avatars)

Is there a way to disabling the changing of avatars and sigs on certain users or possibly a way to set it up as a secondary usergroup so that they are unable to change it?

Thanks in advance.