> Legally speaking, a lack of case law means the jury’s out. But for brands striving to connect with their constituency, it’s clear that more explicit permission is needed for brand-based tags (e.g. #calvinklein), or more complicated tags (e.g. #caughtondropcam) need to be used so that the claim of implied consent is more defensible.

Specific tags only solve half the problem. Someone could copy the tag from someone else without being aware of the campaign going on.