There are two ways to get merits.
One legal way is getting them from writing constructive, high quality posts/ topics, try to help as many other users (mostly newcomers) as possible. This is legal approach, and with this one I really think that 5 merits is possible task (might be reached easily with real constructive users).
Second illegal approach is buying merits from others or exchanging them with friends, etc. In the approach 5 merits mean nothing, and need seconds to get them.
As a result of those two reasons, I think that Theymos should ban ability to wear signature for Junior Members.