Don't think there are any sign-ups at the moment, the latest I saw was last year where you could get a bonus 5k points referral for the member and the person signed up.

However, haven't seen anything recently. There was a new member promo (stay 2 nights, get 1 free) but haven't seen it advertised anywhere (many of us here were able to sign up to it anyway, despite already being members and Marriott honoured the promo) - but it just appeared on our account.