Imagine a prehistoric tribe of savages, who only recently became brave enough to get for themselves a fire that falls from heavens, bring it into their cave and domesticate. When it's cold and dark outside, they all huddle together around their helpful but dangerous protector, humming their proto-songs, fixing their proto-clothes and probably munching their proto-processed food until most of the tribe falls asleep and only the guards would spend their shift watching over the fire, lest it died or tried to spread too far around.
Now imagine that this tribe begins to be interested in establishing contacts with another tribes. May be they hope to kick the other tribe out of their territory and take their women and stocked mammoths, may be they are afraid that the other tribe would do the same thing to themselves, or may be they are just curious to meet new friends - who knows? In any case, how are they going to look for the new tribe? What would they be looking for?
I can only guess how the savages might think, but I guess that they would probably be looking for an inhabited cave (may be larger and cleaner than their own) with a fire in it (may be larger and mightier than their own). So any time they pick up some fire in the distance, they might send some scouts to find out, if there is any tribe gathered around this only possible source of energy.
Next question, what if somewhere nearby there is a little village where much more advanced civilization lives? (Let's not think how come that the more advanced civilization would not try to bring the savage one to their own level, if only for their own security, by tricking them into selling their savage freedom in exchange for cheap drugs and filling up the lowest possible niche in that other society, being simultaneously a recognized sore spot and a symbol of spiritual simplicity, etc).
This other civilisation, in any case, doesn't need to live near an open fire. They have their fires far away, called electrostations (nuclear or otherwise) and although some people have still work in shifts to watch over the big fire, lest it died or spread out, the majority of these more advanced people gets the energy via almost invisible wires and uses it to power their TV sets, microwave ovens, refrigerators and other devices without which no true civilisation is ever thinkable of.
Imagine a savage scout entering such village at night, when all lamps are out. He (or she, may be it's a matriarchal society) would see strange forms which are impossible to place, occasionally here and there some tiny fires which seem to be too little to warm up anybody, no half-eaten carcasses lying around, no caves with entrances covered by bear- or tiger-skins, no people gathered around a shaman humming some story about afterlife, nothing at all. Only darkness and those spooky lights.
I can suggest that such scout would later tell, "I have come to some dark places. It looks like they take the majority of the territory around us. It's nothing there we could recognize. We might be utterly alone all the way to the end of the world." - end of the world being how far they can go and return before running out of food.
The funny question: what if we are the savages and whatever we now call the dark matter is the infrastructure of some super-civilisation which we can't ever comprehend?
So far, we tried to find the tribes dwelling near the fires of big stars, just like us. But what if there are only the super-civilisations around, and they no longer have to dwell near stars, just as we no longer have to dwell near the open fire, because it would be too risky?
In that case, naturally, taking into account how more advanced that other civilisation must be compared to us, we'll probably spend aeons before ever finding out, all this time possibly being watched ourselves without ever noticing it.
This is completely speculative idea, but so is dark matter at the moment :)
So much for dark matter, as seen from science fiction prospective!