The scan process does not give any information concerning if anyone might still be there or even if it’s been visited before. To find out about such things you’ll need to scan it using d-scan, though a few ships are not visible on D-scan.
If scanning a signature keeps returning a 0% result then you have not pinpointed the source of the signature yet; try increase the scan range, start at 8-16 AU range and go down 1-range tick as you scan the signature. there may be times when a signal source may appear to be in 2 locations, if your scan returns a 0% result on the first one you try then go back and scan the other point. On a general rule of thumb, if you see 2 locations for a signature then scan at the location that is nearest a celestial body.
The benefit T1 Exploration Frigates have is that they are dirt cheap. The Astero is the best Frigate-sized ship you can find and it brings a little defenses, some small tank and decent drones. All bonuses is worth having as it makes scanning easier. Furthermore you can also increase your scan Deviation (more accurate), Strength and Speed by fitting modules, to compensate for low skills or low bonuses on the hull you’re using.