I would definitely not use puppy pads, especially at his size and age. I think that if you set up a routine and make sure he goes out on a regular basis he will eventually start to tell you he needs to go out.

I like to stand out with the dog as they're pottying and say "go potty" or "hurry up" because it's a lot easier when traveling or if you are in a hurry, they know when they have to potty and when they can play/sniff around. I usually reward them going potty with a game of fetch (with Kyra) or by getting really excited.

After awhile I'm sure you'll start noticing little things that he does when he has to go out. Like Sophie said, he'll eventually exaggerate the cues.