If you're in mixer signature campaign, now you don't have anything. There is no need to show initiative. Mixer campaigns is allowed on Bitcointalk as long as theymos won't decide different. If one day he will decide to ban mixer campaigns, then you wouldn't have to make decision to leave campaign - all mixer campaigns simply would end then.
What theymos told to staff members is different story. Bitcointalk staff isn't same thing as regular members - they can be considered as employees of Bitcointalk. Emplyees of Bitcointalk advertising ''money laundering'' related stuff - it can bring problems for Bitcointalk. While regualr members can continue advertising basically everything, not just mixers, but also all kind of scams.