Can you tell exactly what do you want to advertise. By looking at description, maybe you can try to post your service announcement on Micro earnings board to get some views.
Your post isn't suited for this board, it would be a better fit in the beginners and help or Meta board as it's an inquiry about the forum.
I think it's right board to ask such question.I'd be curious to know the comparative exposure you get for either option. The last winning auction was 0.16 for 7-9 days. For 50 sig posters they'd all be getting 0.0032 each and I'll bet most wouldn't bother getting out of bed for that.
Good question. There we have exact stats of every ad slot:https://bitcointalk.org/adrotate.php?adstats. But we don't know exposure of signature campaign, because it's different for every campaign and depends on many factors like number of participants, quality and number of posts, paid boards and etc.
But I'm sure that you would find participants by paying few thousands satoshi per post, for example Bitvest campaign paying just 5000 Satoshi per post and still they have lot of participants.
