It can be a delicate subject. For those in favor of fostering religious vocations in young people (or at the very least, not discouraging them), there are several ways to go about doing it. Two approaches seem to be the most common. Some ask point blank, “Have you thought of being a priest/sister?” Others will quietly observe and pray for the person to be open to God’s Will in his or her life.
For those on the answering side of the question, they’ll either take it very seriously (wondering if they do because someone asked them, making it a sign from God), get angry and feel insulted, or casually dismiss it.
There isn’t a blanket right or wrong way to approach someone about a potential vocation. It really depends on the person, his/her temperament, and how you think a comment would be received.
When I was younger and would go to Eucharistic adoration and daily Mass my grandfather would mention a potential religious vocation. When he saw my brother’s love for God and faithful service as an altar server he would mention the same to him.
We handled the remark differently, based on our temperament. My brother would politely say, “Maybe.” I would protest and get on my soapbox, declaring that every young person who makes adoration and daily Mass part of their life shouldn’t be made to feel like they need to become a religious.
Yes, it’s true that on a rational level it makes sense that those kinds of folks could be good candidates for religious life, but it’s also important for our Church and our world to have church- and adoration- loving people who aren’t religious. Still, I’ve also heard that comments from others encouraged priests to pursue their calling.
So the moral of the story is not to consider whether you’re more of a questioner or a silent pray-er but to consider which approach is best for the particular person you believe may have a religious vocation.