They also make temporary tattoos! Just place the tattoo on his hand or arm.

http://www.tattooswithapurpose.com/ordertattoos...

There are many more sites you can find these types of tattoos at as well.

I think a shoe or backpack or anything like that would be too easy to take off! Maybe you could attach his information to the inside of his pants or something. Shoes come off way easier than pants do, and it would be horrible to lose your son and only find a shoe or a backpack abandoned somewhere. It's a scary thought.

https://www.amazon.com/Vital-ID-Safety-Sport-Sh...(Phone number can only be seen by the question and answer creators)&sr=8-1&keywords=id+for+shoes

I used something similar to this. I liked that it went on her shoe instead of a bracelet or necklace.

It is a website called angel sense that has GPS locator wearable device that your child can wear and not aggravate him. I believe the device is small enough to attach inside of clothes, shoes, or even in back pack. I hope this helps.