First holiday abroad for my 4yr old son

My husband and I are taking our 4 year old son on his first holiday abroad.

My son has ASD. His speech is very poor, and his understanding even more so. He can communicate to a certain extent with people he is comfortable with.

My issue being, I want him to have some ID on him whilst abroad. So if God forbid we do get seperated, someone will be able to know his details etc. Has anyone got any tips or hints on best way to do this? He won't wear a wristband or lanyard.

Any suggestions will be greatly appreciated x