I feel called to be a pastor. What sorts of things should I be looking for to confirm this possible calling?
That's a good question.
1) Be looking for a strong and continually recurring desire.
In other words, this is not a flash in the pan desire after some inspiring speech that somebody gave. This keeps coming back, and coming back, and coming back—a desire that you cannot shake. It's right to aspire to the eldership, according to 1 Timothy.
2) Be looking for some gifts that are needed in pastoral ministry.
Gifts of teaching are required, for example. And a certain kind of wisdom with people. So look for those gifts. Cultivate those gifts. Do what you can to exercise those gifts.
3) Look for confirmation in other people.
When a man puts himself upon a church where a church is not delivering messages of confirmation, he is probably out of touch. He may not be. There are a few exceptions where a prophetic voice rises up and is hardly recognized by anybody in the church as a prophetic voice. But by and large the church confirms the gifts given to the elders and the pastors.
So what that means is that you're leading a small group, you're trying to share the word to encourage people, and people are getting help, and they're telling you so ("That was encouraging!"), and they're coming back. They want to get more. They find your presence to be life-giving rather than life-taking.
When people start to drift away from you rather than being drawn to you to hear or to talk or converse, then that might mean you should think, "Hmm. How can I minister to a congregation if they're not getting help by me?" So the third thing is confirmation.
4) Then I would look for circumstances to confirm that sense of calling as well, opportunities that emerge.
Soak your life in prayer, immerse yourself in the word, and stir. And the aroma that comes out of the pot will blow in a direction and you follow it.