Most feral cats are not adoptable without a lot of work, and it sounds like you might not be the right person for that at this point in your life. However, unusual behavior for a feral might indicate a chance the cat is not a feral. 3 years ago I was able to get a presumed feral to eat from my hand the first day we tried. On adopting her, we learned she was a 3 year old neutered female, and concluded she was very likely a stray, not a feral (no catch and release programs around here I'm aware of).
And of course, not everyone puts a collar on their cat. The girl we rescued removes collars, and we just dont bother with it. We arent the only ones around here. There are several seemingly healthy and well nourished cats without collars that roam around. Other times, there is someone that feeds outdoor cats, and their efforts may have already made the feral cat somewhat trusting.
You should approach the presumed feral slowly with food. See how close you can get. Toss food in between if the cat wont come all the way. If your able to get the cat close, and especially if it will eat from your hand, then stray or indoor/outdoor house cat is more likely.
Bottom line: if its appears to be well nourished and approaches relatively easily, I'd leave it alone -- it likely has a home. If it appears under nourished but approaches relatively easily, you could consider adopting. If it remains very wary, then consider if you are really the right person for this sort of project at this point in your life.