add a "reject the signature" link

[tttp]

for campaigns/org without strong security action/supporter confirmation AND with either doi/thankyou:

add as a footer: "You aren't {{firstname}} or you didn't sign? cancel the signature", that would

1. decrease the counter
2. process as a "bounce", ie generate a new event flagging the email as invalid

rationale:
pro: it might be a way to implement the accuracy principle (GDPR article 5.1.e) AND even more strongly prove the supporters are legit without going as radical as the action/supporter confirmation
con: I don't have a strong argument against

implementation details: it should be a two steps process (eg clicking on the link isn't enough, because some email clients do it automatically) AND http get is idempotent.