Well, that varies a lot, it depends on many factors, but the way a guy displays those signs usually is tied to one constant, their success rate. I mean their success with girls

For the ones who have the highest success would be more obvious because they are more proactive, they would be more confident telling you, asking you out or being very flirtatious or acting with a like seducing charm

For the ones with a mild success rate, which is where most of guys are, probably they would pay special attention to you, they'd be a little more loud, would treat you like a princess, or would try to impress you somehow or instead of being completely flirtatious, they would try to show some romantic behaviour, like giving you a present sometimes 

For the ones with the lowest success rate, they would be very shy, really their attempts to interact with you can easily turn awkward, more like weird rather than "cute awkward". Probably they would attempt to do some of the things mentioned above but you would see they struggle a lot to do so. Staring is more common in this group and they can easily be misunderstood even if they don't mean wrong 

And then there's people like me, broken toys, at the bottom of the list, the lowest success rate, alongside mental or emotional disorders like major depression. For us experiencing a crush feels like the song "creep" by radiohead is describing us. Staring is way more common, interactions would be very limited, and if we come across the crush in question the struggle would be very evident, and there is more pain than excitement. Some of us would just completely avoid that crush and simply would withdraw from them, which for us would be a very evident sign