Smiling at him, and letting him know you’re happy to see him is the first way to let a guy know you’re interested. Small talk is a wonderful way to be friendly without being overly forward — and if you’re really interested in him, and you’ve just found out he’s the owner’s son, at a resort where you’re vacationing, you may want to ask him about himself and the resort. “I understand you’ve grown up here,” is a great ground breaker, and you can follow up with, “It must be wonderful to have a vacation place any time you want!” If that isn’t your style or doesn’t work for you — at least you kind of get where I’m going with this line of conversation.
Be happy, upbeat, and interested, and he’ll respond!