Does it apply if you don't say that you are posting under the license? It may be implied, the intent is reasonably clear, but an argument of ambiguity can be made. You're merely linking to a license.
Does it apply if the link label mismatches the license? CC by-nc-sa does more than deny commercial AI training. It requires attribution, requires general non-commercial use, and requires share-alike.
Personally, I prefer when it's at least differently formatted to indicate it as a footer and not comment content. I've seen them smaller and IIRC italic on other commenters, which seems more appropriate and less distracting and noisy [for human consumption]. When the comment is no longer than the license footer… well…