Get yourself a spray bottle and squirt the kitty with water. Just the sight of the water bottle totally has my indoor cat trained ;)
I care for a feral cat that lives in our neighborhood. When he first came around, there were a couple other cats too and it was clear they were not ferals but I was unsure if they might be strays. I took the Trap/Neuter/Release (TNR) class and got the trap. With TNR you trap the cat and drop it off for neutering and shots then you return it where it was. This is the most effective way to reduce feral/stray cat colonies.
Step 1 of TNR is to notify all your neighbors for several blocks that you are going to trap cats. Lo and behold, the 2 I thought might be strays were actually pets that lived on the street behind us. After that I only rarely saw those cats and one began sporting a bright orange collar. I suggest you try the “note on the collar”, if the owners are at all responsible they will curtail the roaming. Most likely they won’t though. In that case that I suggest water.
I don’t know why some people think it’s ok to allow their cats to roam and annoy all their neighbors, but in my experience is that there is no reasoning with them. The most common explanation I hear is that their cats would go crazy if they couldn’t go outside. The 2 cats I’ve owned were used, previous indoor/outdoor cats and both adapted to being indoor only very quickly and gratefully. A roaming cat is exposed to all measure of bugs and disease from other cats and wildlife, can eat dead, spoiled or poisoned things, are at risk for being attacked by other animals or people and being run over by cars.
My feral is very large and he went right into the TNR trap which was baited with tuna. However, he’s very large and the door didn’t get closed all the way and he was able to escape. He didn’t come around for about a week after that and would never go near the trap again. He is still intact and 4 years later getting fed twice a day when I feed my pets. The local bird and squirrel (yes, I have seen him dining on squirrel twice) population thanks me for it.
I used to allow him to rub against my legs (this after about a year of trust building) but he has bitten me on 3 occasions so I don’t allow contact anymore.
All you folks must live in or very near the cities; out here the only feral cats that are ever seen are the ones that have mutated into solid killing muscle, saber toothed hellcats.
Any tabby type that is dumped by an idiot or strays from the house is just coyote food. The ones that survive in these mountains don’t much like people and are very hard to spot, much less catch.