Well, I have two experiences to share, first in entering the seminary, and then in leaving the seminary.
The key point in me deciding to enter (I was 18 and right out of high school) was that I really wanted to serve God in some capacity. However, I wasn’t sure if God wanted me to be a priest. In speaking with another seminarian, he said, “If you’re curious, go [to the seminary]. You’ll know if you’re supposed to be there.”
So I entered. And at the end of each year, I would pray, “Well, God, do you want me to come back?” And until my junior year the answer seemed pretty clear: Yes.
My senior year, though, the answer was: “No.” I had a sense that God had called me into the seminary, and now he was calling me out. I left, deciding that I would take a year out of the seminary, and then decide if I wanted to go back.
Well, I’m now married, with a kid on the way. It doesn’t look like I’m going back anytime soon.
In my experience, there haven’t been strong signs. Just the gentle nudging of the Spirit.