In this set, Mark's passage is sometimes claimed to be the "odd man out". Is Mark to be set against these other verses? First note the parallel in Matthew 16, in context:

> He answered and said unto them, When it is evening, ye say, It will be fair weather: for the sky is red. And in the morning, It will be foul weather to day: for the sky is red and lowering. O ye hypocrites, ye can discern the face of the sky; but can ye not discern the signs of the times? A wicked and adulterous generation seeketh after a sign; and there shall no sign be given unto it, but the sign of the prophet Jonas. And he left them, and departed.

Mark is preserving a shorter version of this episode; does he mean to say that Jesus would not perform any miracles at all? Hardly, since he has Jesus doing them in plenty. A key here is that this account comes right after the miraculous feeding of loaves and fishes -- in other words, Jesus has already performed a massive sign, and the Pharisees do not accept it. They doubted not Jesus' ability to do signs, but their origin in God.

Note that the Pharisees ask for a sign from heaven (the words "from heaven" were often a circumlocution for "from God"; but this could just as well mean "from the sky") -- not just any old sign. This is the context of Jesus' refusal. The remaining verses are therefore not in contradiction.