Two ways of handling this problem - one is to have a system that he won't lose. The medication-alert bracelet or medallion on a chain is one way. The other way is to use something disposable, so it doesn't matter. We kept the sheet of school book labels in the car, along with a marking pen. Every time we got out, we stuck a label or two on difficult child 3. The brightly coloured velcro and elastic thing on his wrist, we took off his wrist when he got back to the car and fastened it to the head rest of the front seat. Then when we got out of the car at the shops or anywhere else, we would fasten it on him. The velcro strap was designed so he couldn't take it off himself easily.
Someone suggested hospital name tags - a possible problem with this, is if he has had any unpleasant association with hospitals. husband asked me to share an incident with you all - his train club sells rides to children and adults, but there are often birthday parties there and the birthday kid rides free. They generally use a stamp on the child's hand but these tend to rub off by the end of the day. So someone suggested using hospital name tags. But one birthday boy turned out to have just come out of hospital after prolonged chemo for leukemia, and having to have a hospital tag was upsetting him, so they used the stamp instead and from there, stopped trying to use hospital tags. We're back to using stamps.
Marg