People kept talking about tagging the participants, or shaming them, without acting so I might as well do it.
Start tagging them just from now maybe a bit harsh, atleast let them know and warn them for few hours, if they denied your warning and still wearing their signature then you might start tagging them.(just my opinion)
Isn't tagging them also a way of warning them? I mean those tags can be removed or changed to neutral anytime the issue with that account is resolved. In this case, withdrawing from the signature campaign.