Since Mechanical Turk requires you to pay, I feel like it would cost more for that than the sig campaign could pay out.
I would doubt this, mturk often has very low paying "jobs" often only a few cents (sometimes only one penny). If you have a senior member then you can earn the Bitcoin equivalent of ~$0.25 per post in a pay per post campaign and at least double that in a fixed rate deal. You could easily make at least $0.20 per post if you successfully did this. I did think about this a little bit when I started farming accounts but never tried it. One issue that you will have is that you will need to review responses prior to posting them and if you don't post quickly enough after receiving a submission you would need to review the thread to ensure the same thing has not previously been posted. These steps could easily take up as much time as it would otherwise take you to post yourself, especially considering that there is a good chance that you would need to reject a percentage of submissions.
If you are not careful enough about moderation of which submissions you accept then you would be risking your accounts get banned for insubstantial posts + paid signature.
It would also be possible that a moderator could make a good submission, you post it and then the fact that you are using mturk would be known and this fact would probably be frowned upon.
