What should I do about items like jewelry from my mother with dementia?

MC recommended that I remove mom's wedding bands and expensive jewelry because of loss and "shopper" residents. She lost her sense of time.
I told her that I planned to take them for cleaning and repair. Afterwards any time she asked I would tell her they were still in repair and then she stopped asking.
I did keep some inexpensive necklaces in her room but that was all

Because my mother was constantly “giving” us things, then claiming said things were stolen, I placed a large box out of sight and told my family to put everything from her inside. That way, there was no searching our house to make it reappear. Consider attaching a paper and pen so everyone can log what they put in and take out.

Eventually “misplacing” changed to “hiding” as she was determined to outsmart the imaginary thieves that robbed her home every day. I noticed that she started to become very angry when I found her stolen items, as if she wanted to be correct that they were gone more than she wanted them back. It was a subtle but odd transition. At that stage I stopped searching her house and didn’t return anything from the box, but simply said “Oh, I’m so sorry to hear it’s gone.”

If the things are of any value, sentimental and/or financial, I would not give them to her. You need to have a vague response ready for these requests. Hmm, I don't think I know where that is. Oh, I'm sorry but last time I looked for that for you I could not find it. I'll double check.

Put away (far away) all the things she has given out in so far as possible. Tell her that you will check on items missing. If her dementia is severe she will not hang on to these ideas, but given that obsessions are common she may return to them. There is little you CAN do, and returning things to have them lost of given away isn't really a good idea. I am sorry she is going through these things. Best to deflect and let things fade away in so far as you can. It hurts to have to fib, but there is little else to be done. This was so common with my partner's Mom at the end that he and I now laugh when something goes missing and say "Wilma took it" as his Mom used to accuse her faithful and much beloved housekeeper of taking her things for the last years of her life. She would hide things so "Wilma can't take it" and then they were gone. Only to be found after her demise in the most odd places you can imagine, everywhere from the slow cooker to the back yard shed pails.

Your mother has dementia, I assume, since you put your question in the Alzheimers & Dementia category. With that said, losing things & forgetting she gave you certain items goes with the territory, unfortunately. If she's wanting a bunch of expensive jewelry and losing track of it, you could buy her some inexpensive costume jewelry like cubic zirconia rings and things and hand those out to her so if/when they're lost or given away, no big deal.

My mother had advanced dementia & lived in Memory Care Assisted Living. She used to insist 'all the ladies have BIG BIG BIG diamonds except me, so I want mine back.' She had a 2.5 carat solitaire ring I kept at my house for security/safety reasons. There was NO WAY on earth I was going to give her that ring to wear b/c I KNEW it would go missing and then she'd have a meltdown, so I brought her some other inexpensive 'diamond' jewelry like bracelets and rings for her to wear to 'compete' with the other ladies who wore jewelry.

If you are new to caregiving an elder with dementia,  I suggest you read this 33 page booklet (a free download) which has THE best information ever about managing dementia and what to expect with an elder who's been diagnosed with it.

Understanding the Dementia Experience, by Jennifer Ghent-Fuller 
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Jennifer is a nurse who worked for many years as an educator and counsellor for people with dementia and their families, as well as others in caring roles. She addresses the emotional and grief issues in the contexts in which they arise for families living with dementia. The reviews for her books are phenomenal b/c they are written in plain English & very easy to read/understand. Her writings have been VERY helpful for me.

The full copy of her book is available here:
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Best of luck to you.