I'll PM you a link to a store. It is American, but it doesn't take too long to come over.
It's profits go to the Gastroschisis Foundation which is lovely, too. Our kids have a very comprimised immunity.
It has all sorts, bibs, shirts, onesies with different slogans on them such as "No Germs allowed" "Warning! Hands Off! Immune Comprimised" "Respect my Space! Dont touch" "Look but don't touch" "Wash your hands before touching mine" "I know I'm cute but please don't touch"

You could always put up your own sign using one of those slogans.