Not only that Just find the right campaign Where you get good amount of payment and check is there Escrow is working on that sig campaign, and wear their signature and pass a post in a Signature campaign's thread. and most important don't join to the negative trust guy's sig campaign, because he may cheat us.
Actually in service section all signature campaign using escrow, maybe 1 or 2 campaign don't use escrow like secondstrade, but secondstrade already got trust here.
OPAIR ddoesn't hold any escrow too but Lutpin is the one who managed it and i think is safe.. IT is also important to check what kind of site that the campaign are promoting.
for example a scam site, do you think they will gonna pay for the rate for that reputation? and also the manager of the campaign is an important factor too.
goodluck on choosing campaign!