Sentience is such a subjective...er...subject. What is intelligence anyway? The humans of Earth, for example, seem to be doing quite well without it. And civilization? That's even more of a shot in the dark. But like art and pornography, you know it when you see it. Sometimes, there are People, whether they are fleshy mammals keen on burning carbon-based fuels or gelatinous blobs of tissues who have been able to invent hyperdrives despite a complete lack of either opposable thumbs or the desire to actually use hyperdrives to find out if they are not alone in their universe. Sometimes, they are simply very patient and deeply meditative stands of trees with surprisingly witty senses of humor. Just ask their fungal neighbors! The point being is that these beings are the ones most likely to attempt to have a conversation with. Or avoid, if they'd rather vaporize you or use you as a replacement fuel source to their carbon-based ones.