How can troll posts be How can troll posts be recognized?
No Imagination - Most are frighteningly obvious; sexist comments on sports fans, blasphemy on religious groups .. I kid you not.
Pedantic in the Extreme - Many trolls' preparation is so thorough, that while they waste time, they appear so ludicrous from the start that they elicit sympathetic mail - the danger is that once the group takes sides, the damage is done.
False Identity - Because they are cowards, trolls virtually never write over their own name, and often reveal their trolliness (and lack of imagination) in the chosen ID. As so many folk these days use false ID, this is not a strong indicator on its own!
Cross posting - Any post that is cross posted to several groups should be viewed as suspicious, particularly if unrelated or of opposing perspective. Why would someone do that?
Off-topic posting - Often genuine errors, but, if from an 'outsider' they deserve matter-of-fact response; if genuine, a brief apposite response is simply netiquette; if it's a troll post, you have denied it its reward.
Repetition of a question or statement is either a troll - or a pedant; either way, treatment as a troll is effective.
Missing The Point - Trolls rarely answer a direct question - they cannot, if asked to justify their twaddle - so they develop a fine line in missing the point.
Thick or Sad - Trolls are usually sad, lonely folk, with few social skills; they rarely make what most people would consider intelligent conversation. However, they frequently have an obsession with their IQ and feel the need to tell everyone. This is so frequent, that it is diagnostic! Somewhere on the web there must be an Intelligence Test for Trolls - rigged to always say "above 150"d?
How to react to a troll ?
DON'T, JUST IGNORE THEM.