"anonymous posting" can mean a number of things:

1) a non-member posting without outing in any name, so they bcome through as GUEST

2) a member logging out and coming in as a GUEST without any name

3) a member logging out and coming in with a different name from the one thet normally used

4) a member logged in, and using a pseudonym which means they are not identifiable with somone in the real world.