Not exactly the same but I've had a discussion around a similar topic with a Canadian immigration lawyer. We were put in contact by a mutual friend and the lawyer was looking for an email provider that was hosted in Canada and didn't rely on any US-based services (e.g. spam filtering). I asked him about the requirement and he pointed out that it was legally impossible for him to simultaneously comply with the USA PATRIOT Act and Canadian data protection/privacy laws. The US Gov't could compel his email provider to disclose solicitor-client privileged data with a gag order, and by not telling his client he would be breaking Canadian law.

By putting statements like what you're proposing in your TOS or marketing material you are potentially setting yourself up for a situation where it's now impossible to comply with all applicable laws. As others have mentioned, Australia passed legislation preventing you from disclosing the existence or non-existence of specific legal documents; they're at least warning you up front that the canary itself is illegal. The solution is to not make marketing statements that would become fraudulent in a situation where you can't legally retract them, unfortunately.

Edit: since lawyers are mentioned here... if the lawyer who is telling you that you need to remove the line from the TOS is the same lawyer who told you it was ok to put the line in the TOS... you should probably find a new lawyer because they didn't think through the consequences of approving it in the first place.