A tendency to make posts in order to boost your post count, and you have an ad in your signature, particularly one that pays you per post. There is no secret invisible line that you shouldn't cross in terms of numbers, it's mostly subjective. 

There are people who just don't post very well in general, post "too much", or don't really have anything to say, they just like to participate in the community and post. This itself is fine. But when you add an ad to these kinds of posters, it's difficult or impossible to tell if they just aren't quality posters or if they are attempting to boost their post count. I used to err on the side of caution here because I do not want to ban the former, just the latter, but too many of the latter are slipping through the cracks because it's very difficult to gauge someone's intentions. This is the main thing that has changed lately.