I think that's the easiest way to put a sticker over something, but for sure, other methods would help you remember.
Actually there are many options. The sticker option is the easiest. If continue to develop this idea, then it was possible to buy hardware wallets in different case colors. For example, Ledger Nano S can be bought with different colors (about 5 shades if I'm not mistaken). At Trezor, can also choose the color of the case: black and white. As far as I remember, this does not affect the cost in any way. But this is when you are just going to buy wallets.
If you already have hardware wallets, then I see the simplest solution in crwth's idea with a sticker.