I agree with @bitmover but I think that the continuity of signature campaigns comes from gaining loyalty more than increasing the number of users, personally I used thechange and exch because of their presence in the forum which gave me assurances that they will not scam me for amounts less than $1000.

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To get an accurate answer, it may be better to review the signature campaign data for the last 7 years, I think that for many years mixers and casinos were the only ongoing campaigns and no major services related to bitcoin have been announced here for a while.

Apart from mixers and casinos, the last long campaign I remember was coinpayments.net and Gunbot