I can't recall if it's against the forum rules explicitly, but it's definitely frowned upon to post crap like "+1" and other one word replies to things, especially if you're in a sig campaign. Shitposting.
I think those are covered under rule 1 of the forum rules:
1. No zero or low value, pointless or uninteresting posts or threads. [1]
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1. Such posts like "SELL SELL SELL", "I agree", "+1", "Support", "Watching", "Interesting", "LOL", "SCAM", "LEGIT", "FAKE", other one word posts, posts consisting mostly of swearing, quote pyramids,useless introduction threads, threads about a topic already recently discussed in several other threads.
Sorry sorry sorry!!! I just got home from work and was too lazy to actually find where the rules are and look at them. Thank you, I appreciate that and I mean it. This is actually one of the things I like about bitcointalk--I'm a member at a few other forums, and the amount of crap posts is staggering. Sometimes you can scroll through many pages of just quote pyramids and just emoticons and it's just ridiculous.