There is not exact amount on how much you can earn through signature campaigns since people are joining from time to time and the amount you'll receive will also be lesser than the time you join but you can estimate it through the bounty budget and the ICO price of the coin you'll get.
Actually it varies on the manager and their rules also, because everything was written on the front page of the campaign and they will find the rules and the salary rates per rank of members. But if you are planning on joining a bounty campaign the rate would still varies on the manager sides and the rules.