I have no idea who sent me these! Pincushions that go on your wrist?

Going by the dollar sign, your sister in America sounds the most likely source.

Incidentally, free items received via Amazon do not always result in fake reviews. I was sent a hairdryer once and as I had not ordered it I emailed the sender to ask why they had sent it. They said it was just random and I should use the hairdryer and then give it an honest review. I did, it was a good hairdryer and I'm still using it.

Wrist supports for when you use a computer mouse?

Where they from Amazon?
If so there is a scam whereby sellers send out cheap items to random people and then post fake reviews.

Ooh, ExDancer, the arch support idea is a distinct possibility - they do fit. I’ve had plantar fasciitis in the past and still get the odd twinge. Did I order them in some mad forgotten moment? A bit worrying if so!

A sister in the US is also a possibility, but she won’t be up and doing yet, to ask.

I looked up ‘brushing scams’ but they weren’t from Amazon, it was a very small package with no indication of the origin and no paperwork inside. The price was listed for customs as about $3 though.
Still at a loss!
I suppose I should check cc statements to see whether I’ve been charged for something I haven’t ordered.
Very weird!

That's what the picture suggests, pincushions although they don't seem very well padded.
If they are quite thin, could they be something for using on your feet to alleviate lack of cushioning on the sole, or to help with dropped arches?
Is the postmark any clue? No invoice? No request for a donation from a charity? (I was once sent an umbrella with a donation request - a bit risky I thought, but I sent one anyway - it was a nice umbrella)

Look up "brushing scams". Could that be it?

They look like they might be dusters that slot on to your hand. More for polishing than pins and needles.