Depends on the relationship between the "saluter" and the "salutee", and on the sex of the "salutee". "Ciao" is familiar, and in some regions people use terms of endearment even when they don't know the people! So "Ciao, bello" is appropriate if the saluter knows the salutee well, and the salutee is a male. "Ciao, bella" is OK for a female salutee and could mean 1) the saluter knows the salutee well; 2) the saluter is a rude construction worker and underlines the salutation with a whistle!

Floriana