I strongly think it is and obv. this lowers the overall quality of this forum as a source for useful information. As soon as a newbie asks a question, sig spammers start crowding the topic with their 99% sensless/false/bs answers. Some (most?) of them didn't even understand the topic!
@Theymos: The problem is not created by the sig spammers, but the system allowing it. There might be a point where Bitcointalk will be rejected by the users, when you can't find the information you are looking for, because it's hidden in a flood of trash.
The voting on this topic seems to be unanimous - 100% for yes (14 votes) and 0 for no. Apparently everybody (who reads the meta threads) thinks that this is a big problem.
I don't think it's a big problem, but I do believe that it contributes to the low quality of many posts.
It's hard to judge how much the possibilty of earning money through signature campaigns contributes to low quality posts, since there's a lot of people who are unaware of these making terrible posts anyways. This is in part due to the large profits achievable in the crypto markets, so there's inevitably going to be a strong draw towards people who want to make quick money. Most of those are simply very impulsive and not very bright, leading to off-topic random nonsense en masse.
I personally couldn't really care any less though. In fact, the state of the forum does help with due diligence, albeit in a peculiar way.