A foster cat is an escape risk wearing borrowed paperwork. She is in an unfamiliar home, she may bolt at a door she does not know, and the people who legally know her belong to a rescue rather than to your household. Her identification therefore has to do two jobs at once: get a finder talking to the human who is actually there for her, which is you, and make clear that a rescue also stands behind her, so nobody assumes she is a stray to keep or a neighbour's cat to feed and forget.
The Collar and Tag She Actually Wears
Fit her with a lightweight breakaway collar, the kind that releases if it snags on furniture or fencing, because a foster exploring a new home will squeeze through gaps a settled cat would ignore. Check the fit with two fingers between collar and neck, and check it again after the first few days, since nervous cats often lose a little weight in a new placement. A collar she tears off in the house is information too, so keep a spare ready rather than leaving her unmarked while you shop for another.
The tag on that collar should carry your phone number first, because you are the person who can collect her within the hour, plus a line identifying her as a foster with the rescue's contact details. A short line on the tag identifying her as a foster cat, naming the rescue as the second call, tells a finder she is owned, loved and expected home, and stops a well-meaning neighbour from adopting a cat who already has a placement plan. Keep the engraving short and legible, use a number you actually answer, and replace the tag if the lettering wears smooth.
Photo, Description and the Rescue Chip Question
On her first day, take a current photo and description and keep both where you can reach them fast: clear shots from both sides, one of her face, and a written note of the markings a stranger would spot, such as a torn ear tip, a white bib or an unusual tail. Update the photo if she stays for weeks, because a thin arrival can fill out noticeably and an old picture slows down anyone trying to match a found cat to your description.
Microchips need honesty rather than enthusiasm here. A foster may already be chipped to the rescue, so check the paperwork the rescue gave you and have her scanned at a vet visit or by the rescue to confirm whether a chip is present and what number it carries. A scan yields the chip number only; the registry holds the contact record attached to that number, and for a foster cat that record is the rescue's record, which stays the rescue's. Do not re-register a chip that belongs to the rescue into your own name, and do not assume that noting her number in her profile changes anything at the registry, because only a change confirmed back with the holding registry counts. If she arrives unchipped, that decision belongs to the rescue too, so raise the question with the rescue rather than arranging it alone.
If She Gets Out Anyway
Tags and photographs are the first layer, not a guarantee, so treat any escape as a same-hour problem: search the quiet hiding places near the door she used, tell neighbours she is a foster wearing a tagged breakaway collar, and pass her photo and description to the rescue straight away so their network hears about her too. If she slips out despite the tag, an alert sent through Lost Pet Alert System reaches nearby owners across the local network, and the person who finds her is given a direct line to message you, with KinsLe keeping that route open from her profile.