Cleveage isn't indecent, matter of fact I love it.
Rule for posts:
The Rules said:
All humanoids in posted or linked to pictures or sites must be clothed.
Rule for Sigs/Avatars:
The Rules said:
Avoid indecent/sexually suggestive content in signature and avatar especially, since users do not have the option to block only your signature/avatar.
If you post that image in a thread, I can avoid it to prevent from getting in trouble at work or wherever. If you put it in a signature or avatar, I cannot avoid it, because any thread you've posted in will have it. This is why the rule is more strict for signatures and avatars.