Oops. 

Long story short, we picked up a stray ferret recently, no sign of an owner but she's just a young thing really. I'd stake my life on her not even being a full year old. 
She's super dinky, and ridiculously pretty, teeth and coat all in good nick and she's not skinny at all. She's eating everything we put in front of her, kibble, raw chicken, cooked chicken, eggs, chicks, lactose-free milk, cat treats... everything, so definitely not fussy.

She's pretty friendly too, a bit shy but definitely not a biter.

But she's very podgy around the tummy. Not crazily but she's definitely got a belly going on. We've also noticed her nipples are quite prominent in comparison to my own jills (I have four of those, and five hobs).
She's got a lot of scruff-marks around her neck too, which could easily be from the attention of a male. It's not exactly ferret-pregnancy season but she's so young and it's been so warm I wouldn't say it was impossible for her to have had a late oestrus.

Honestly I'm hoping she isn't because she's just a baby herself. Plus, she gets on really well with one of my other jills and I would love to let them play together ASAP, which I obviously can't do if she's pregnant/nursing. At the moment she's alone in a cage in my study.

We have a vet appointment for Friday where I'm hoping they can tell us definitively whether or not she is, but I wondered if anybody had any good ways of knowing whether or not it's likely that she's expecting?

You found a stray ferret? Its so nice you gave her a helping hand. I hear that in Europe there are a lot of stray ferrets and ferret x polecats. However, her being so small I would guess she was a pure ferret. If she really is feral, she probably hasn't been spayed and is likely pregnant. I heard raising baby ferrets is more work than raising some other kinds of animals, so make sure you do research. Again, I'm so glad you took her in. Best of luck with her! : )

I didn't actually find her personally, someone reported that they had caught a ferret and we went to pick her up for safekeeping. But yeah there are loads of stray ferrets over here sadly, lucky for this one she got caught. Quite a lot of my guys are strays that came to me one way or another.

Oh yeah, definitely a bit worried about babies, I once took on four five-week old hobs and that was madness! Baby ferrets are so messy!
Very much hoping it's just a phantom pregnancy or something!

Took her to see the vet today, the vet says she's 90% positive she's pregnant (if not she has a very full uterus for another reason, so hoping it's not that) and we should expect babies in 3-4 weeks.

Scary!