Buy a collar, then make a card of moderate size (strong material) and write it on it.
* * * (cat's name) If found, please return it to Unit * * * at Building * * * * on * * Road and put it in a waterproof pouch. It can also be glued on the card with transparent glue, which can play a waterproof role and prolong the service life. Then hang the card on the collar and it's OK (use some strong thread and don't fasten it)
Simple, buy a leather collar, write it with a clear silver pen or carve it with a knife, and others will know it's the owner's phone.
Of course, if you want to be elegant, it's not bad to buy one from Taobao and other places, and it won't be too expensive ~ ~ ~