That’s why they sell breakaway collars with quick-release buckles, they’re made specifically so animals don’t hang themselves.
http://www.petco.com/product/123278/Petco-Classic-Break-Away-Cat-Collar.aspx
I suppose an alternative would be to stencil “IS THIS YOUR CAT? CALL ME AT xxx-xxxx” in washable spray hair dye on the side of Creamsicle. 
She knows about breakaway collars.
I’m sensing the collar in non-negotiable, but would the SO be willing to go look at some in the store? My cats’ collars are so break-away that they come off all the time (scratching, play wrestling, rolling on the floor, etc). Maybe if SO handled some, it would be re-assuring.
I used this technique once to find an owner. Attached the brightest, neon, glittery, rhinestone job I could find to a lovely tomcat. I got a call very quickly. 
Option 2 is have a vet scan for a chip.
I was just at the little market. I said to the woman at check-out, ‘I see you walking on [our street].’ She said, ‘I live on [your street].’ I asked her if she knew where Creamsicle belonged, and she said that she thought it belonged to her neighbour who died in March. She said the neighbour swore that the guy behind her ‘stole’ the cat and had it fixed.
Sounds like she needs a safe landing.
StG
The market lady told me that she actually lived on [her street] at [my street] in ‘the red house’, and that the deceased lived in a trailer next to her. (This is a summer holiday village, and there’s a mix of cabins, houses, double-wides, and single-wides. Not as many trailers as other structures, but we have a single-wide on one side of us.) She didn’t know Creamsicle belonged to the dead woman, and my description was very quick (orange-and-white longhair, kind of tiny) because there were other people in line. I should find her house and ask her neighbours if they know the cat, and whether it is homeless.
My mom’s back tenant, a retired rodent-control contractor named Miss Mousy, spent a good three or four years running from humans… but at the same time always giving us a look of fascination. Now that she’s finally gotten over her fear, she’s an insatiable attention mooch-- If you bring her out a dish of food, she’ll insist on a petting before she’ll even eat.
Creamsicle’s back. Tonka is a little agitated. He’s yowling a little, but not at Creamsicle. He’ll go to the screen doors and look. Creamsicle will approach, but as soon as he sees Tonka he hisses at him.
Long intro through the glass is actually part of the recommended process. Look, no touch 
Eventually, there is sniffing through a small crack, then maybe creamsicle comes in. Take it very slow.
BUT before that… If you decide you want to try this, Creamsicle needs to go to a vet to get checked out. Get his(her) shots and get tested for FIV. Don’t want to give Tonka anything.
Good luck.
I’m pretty sure Tonka has had all his shots, including for FIV. Still, we want to have Creamsicle checked out before letting him/her come into contact with him. I told the SO what the market lady told me. It’s a good lead, but ML said she thought Creamsicle belonged to the dead woman, and she thought the dead woman told her the guy behind her had the cat surreptitiously fixed – which may or may not have happened. Sounds like hearsay to me. The SO said it’s good enough for her; but she had just had some minor surgery and was doped up on Demerol. I want to be sure as I can be that the cat is indeed homeless before I take it in for surgery.
It sounds like she might want to keep Creamsicle. I wouldn’t mind, but I don’t want Tonka to feel slighted. This is Tonka’s home.
As long as Creamsicle doesn’t go after Tonka’s toys, it should be good.
And Creamsicle is one of the most beautiful cats I’ve ever seen.
Creamsicle is gorgeous, and Tonka’s reaction seems fairly normal IME. I bet if you take it slowly, they will adjust to each other just fine.
Right now, Creamsicle is the one that needs an attitude adjustment. S/he hisses at Tonka.
Creamsicle was outside when I got up this morning. I slid open the screen door and she came right in. She looked around and made her way to the kitchen, where she took an interest in Tonka’s dish. Tonka came out from one of the bedrooms, and she hissed at him. He’s just trying to be friendly! I got some food for Creamsicle and guided her outside.
Later, I went out on the patio where the SO was sitting. I thought I heard rain on the roof, but when I looked it was Creamsicle. No idea how she got up there, and she didn’t seem to know hot to get down. I grabbed her by the scruff of her neck and got her down.
You must be very tall.
I stood on the deck. 
I’ve never heard that before and I’m surprised considering two thirds of orange cats I’ve owned have been female (every one of them, male or female, were related though).
Talk to the guy who “stole” her (it can be difficult to find a spay scar - esp on a longhair) and inquire as to whether he “owns” a red-and white (striped) female cat. Have a pic or two in your pocket. If he claims her, and she’ll let you take her by car too a point nearby and then carry (permitted yet?) her towards that house. If she gets agitated, she’s yours. If she goes running to a heart-warming reunion, she’s yours as she decides on some variety in the humans she permits to care for her.
If you suspect neglect, at least have her de-wormed and updated on her shots.
And collars don’t allow a critter to hang themselves - at least not properly fitted ones. Break-aways are for people with over-active imaginations.
You should be able to fit a single finger under the collar without choking the critter (too much). More than that is an invitation to trouble.
We’ve decided Creamsicle is a girl. The SO brought her inside last night. Tonka lay on the ottoman; she stayed within three feet of the closed screen doors, sometimes passing behind the SO, who was sitting on the floor. Tonka came down to check her out. His stance was ‘curious’, not ‘angry’. Creamsicle hissed at him and he sulked away behind the ottoman. After a couple of minutes he jumped back onto the ottoman and lay down. Then he started cleaning himself.
The SO tried to hold Creamsicle, telling her Tonka isn’t going to hurt her, but she was having none of that. She got into the meatloaf position, a couple of feet ahead of the SO and pointing in Tonka’s direction. Tonka was lying prone, and the posture of his head was ‘stalking mode’. His expression wasn’t stalking though, but just ‘alert’. He got hissed at.
Creamsicle got up and went to the screen door where it slides open and sat down. Tonka trotted up behind her. Whenever he approached her before, he was just curious. This time he looked curious and sniffed her tail. She got agitated and Tonka pounced on her. There was a loud hiss, the SO yelling ‘Tonka!’ and then he backed off. I think he must have had enough of being hissed at in his own house, especially by an intruder less than half his size and when he was just trying to be friendly. Creamsicle was let outside. The SO told her that she’s going to have to get used to being in the house with Tonka. It’s nice out now, but Winter is freezing.
You all know Tonka was a ‘long-timer’ in shelters. He’s used to being around other cats. Creamsicle is young and appears to have spent much or most of her time outdoors, so she’s probably used to avoiding other cats.
Earlier in the day, Creamsicle was sitting about four feet away from the French doors. Tonka lay prone and was ‘talking’ to her. Like, ‘Hello. Be my friend?’ Instead of hissing, Creamsicle sat quietly looking at him.
Ooh, I like the war correspondent stuff. 