Is there a way to tell if you're still hidden in the fog of war?

after playing from a while you get a "feel" of what they can see in lane; unless it is warded somewhere they dont know. From my experience, it's intuition. Like when you gank through lane and sneak into the bush, you usually watch for the closest minion. I think the radius of the minions are like 700 or something like that

No, there is no way to see that you're covered by the fog of war by your enemies perspective or not. Most of what you see is intuition based on how the enemy you see is reacting to you. If they are noticeably avoiding the bush or they're glowing (With a slight yellow outline) because they have targeted you it usually means you are being seen. If someone is standing in the middle of the lane unnoticed is because they're on the lookout for another champ or waiting for the minions waves.