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Promoting through signature campaign can only be acceptable if you already has a good budget for your advertisement because signature campaign is so much costly and you might not be able to get the result that you desired.
actually signature campaigns are the cheapest way of advertising your business! you can check out the other ways of advertising prices and you will see yourself.
for example the banner bitcointalk banner advertisement is 0.3
BTC for 1 slot which is only shown randomly among other banners and other site's banners are no better especially with all the ad blocks which will block banners on those sites.
From what i can see is advertising via signature is good choice, and yes its cheapest if you comparing with other advertisment. And you can make a rules for the participant to advertise specifically, there are some gambling company who still used signature ads, and why they still use it, because they have more attention, attraction, and more people to join. because this is the best place to advertise bitcoin business, with smart rules, audience will easily comes.