I agree with the other women's comment. Take him out of pull-ups. If I put my son in pull-ups he won't bother to go at all. If he has to pee on his pants he's more likely to get to the potty. My son is 3.5 and will use the potty most of the time, but never asks to go. I recommend getting an egg timer (to help you remember) and make him go every 20-30 minutes.
Another thing that works VERY well is to take away what ever he's doing in the moment. If he's playing with a truck, take it away and say, "you may have your truck back after you use the potty." Kids are very 'in the moment', so if you take away (and then give back) what ever he wants in that moment he will care more.
I tried using treats before I learned the technique above. Treats only worked once in a while because if my son didn't feel like having chocolate/a toy/whatever in that moment he wouldn't bother to use the toilet. However, he WANTS whatever he's doing in the moment.
I still have no idea how to make my son tell me when he needs to use the potty. He's never been a talker. I just try my best to stay on top of it and make him go every 30 minutes or so.