USS's (as well as the Weak and Strong Signal Sources) are 'areas' rather than objects, so when you drop from SC there isn't necessarily one transmitting source to find, like you would have with a station.
What you should get, if you drop from SC when you get the blue 'safe to disengage' message, will vary. After a few seconds you should see one or more ships, or some canisters floating in wreckage and who knows what else in the future.
If you wait for a while and nothing appears on the scanner then I've very rarely seen 'empty' USS's but the rest of the time there will be something to do, even if it's to run away quickly from a wing of aggressive Anacondas

Edited to attempt to clarify myself. I'm not sure I helped here. Need more Lemsip......