Hmm.. satellites? A planet with 'advanced civilization' would have satellites or other objects orbiting. Also devices that fly - so some radar can pick a plane in the sky? its Transponders? Scan the sea for large floating objects?
On the dark side one should be able to observe lights, and the same locations during the day should have cities (and not i.e. forest fires or volcanoes)?
On the light side one would be able to 'zoom in'/scan the surface and see structures or other shapes that would imply some manipulation of the surroundings on large scale.
How about antennas picking up multiple signals (radio, tv, etc.?)
For the case that it's pre-cities/pre-industry, good luck... Good luck zooming in and spotting 10 'planet-lings' (from Earthlings) with their planet-goats crossing a valley.
Having played A LOT of Starcontrol II though I can imagine that sending small crafts to the surface would help verify suspicions.