The answer to the joke "What is a message printed on a lion with chickenpox?" is, "Sign on the dotted lion." This joke is a modification of the lion-chicken pox joke that goes, "What do you call a lion with chickenpox?" The answer is a dotted lion.
Apart from the obvious play on words, this joke also touches on one of the main symptoms of chickenpox, which is the appearance of lesions or blisters. Once the blisters dry up, they form a scab that resembles dots on the skin.
Chickenpox is a type of viral disease that usually occurs in children caused by the varicella-zoster virus. Apart from the blisters, other symptoms of the disease include fever, headache and stomach ache.