Yes you can, or you can buy copper member and be an active poster in meta, then you already did (promote) it without worried breaking rules,

What you talking about? Why you should post in meta only, why not in other board?
Are you mean be an active poster will automatically get merit to rank up till member, and he can use signature without buy copper membership? You're totally wrong.
Be an active post in meta board not always get merit if your post is low quality and spamming, and also I have seen many member get merit in other board, not only meta.

Keep in mind only put refferal link/websites in signature or personal messages is not done yet, you must follow all the rules again Unofficial list of (official) Bitcointalk.org rules, guidelines, FAQ . If you're spamming and keep promoting in your signature/personal messages, your post will deleted by mod or get red trust