they do work , but there are too many variables to take into account
the main problem - it is very costly and for a website without a proper bankroll / marketing funds it could be better to use other forms of marketing
don't expect a flood of gamblers waving their money from the get go , signature campaigns are more than that:
backlinks , exposure , proof of funds of sorts etc.
and certainly , do monitor the effects of the campaign if you launch it
Signature campaigns and marketing alone can't boost number of gamblers/players if they don't like your product. Marketing and in our case signature campaign, helps business owners to reach to potential customers, as much as possible. Design of sig campaign, participants of sig campaign and business model (whether gambling, exchange or something other) affects the number of impressions.
Did 90 from 100 clicked on signature and came into your website? Congrats, along with possible 1-2 misclick, a lot of users were interested. Didn't they registered/visit your website again? Then seems there is something wrong with product or with both, product and what text on signature promises.
There are a lot of details that have huge influence on marketing. You have to analyze each of them and improve your weak points in order to achieve success.
And oh, I already answered that campaigns work and there are great examples, both, past and current.