I reared 4 kids (2 girls, 2 boys) and have helped train 2 grandsons. Mine were all totally potty trained by 2 (except both boys had a few wet beds after that -- not the girls), so I have some experience. (My mother-in-law said her 2 boys and 1 girl didn't use diapers after their first birthday, but she TOOK them to the potty or held them over a newspaper regularly. I didn't have THAT much patience with it!!)
Your attitude is probably most important. Either you DO expect him to be responsible, or you are 'casual' about it. Neither is wrong or right, they're just 'different'. Just make sure that you're consistent, not 'demanding compliance' one day and relaxed about it the next.
If you seriously think he KNOWS when he needs to go, and YOU are ready to 'get down to business' about it:
1) be sure to praise him (cheer and clap, if necessary) when he does go on the potty (either #1 or #2).
2) don't use diapers at all. They're too dependable (hence the adult brand of 'Depends'). Use training pants or regular underwear and let him wear them wet or dirty for a little bit for his discomfort (as long as he's not getting it on stuff).
3) tell him ahead of time (calmly, not threateningly) that if he 'messes' his pants, he'll have to clean up the mess -- then FOLLOW THROUGH. Have him dump (even 'scrape', if necessary) it in the commode (however YOU would have to do it), have him put it in the laundry or washer (if it's wet bedding, have him go ahead and help with the whole laundry process, washing, drying, folding or putting back on the bed).
4) Tell him when he uses the potty all the time for a week, he can go choose some cool underwear of his very own (then do it).
P.S. Using stickers as a 'reward system' is NOT 'bribery' (which is usually something about 'DON'T do this or that [negative thing] and I WON'T do this or that [negative thing]' -- kind of like 'blackmail', which is a BAD thing) or promising/giving them something that's not really good for them. On the other hand, saying, "If you do 'this' (desirable thing), I will give you 'this' (desirable thing)," it's simply positive reinforcement (like we adults get a paycheck 'if we do this and/or that' at our workplaces), and it's a GOOD thing!