After these replies, the conclusion I get is that on the one hand, it is the right thing to do, but on the other hand, it can be bad because I would be punishing people who are trying to improve their post quality.
I’ll tell you what I do: if only that post is worth meriting and the post history is crap, I won’t merit the post. However, if I see in the post history a changing pattern, even for the last 3-4 posts, I will merit it.
I think this is an argument for increasing the merit requirement for having a signature from 1 to 10.
But if Jr. Member have higher minimum merit (between 3-5) or signature for newbie can't be filled with url/website, that would save people's time.
Yes, theymos said that he might increase the requirement from 1 to 5 merits, and I think this is what will end up happening. There will be always people trying to game the system, but these are steps in the right direction.