While in seminary (actually there and taking classes) and/or doing parish work, the seminarians in my diocese wear clerical garb. Some just wear black suits w/ a collar while others wear a cassock.
I have noticed lately that many of our younger seminarians though, are ALWAYS wearing their clericals, even when they are home for vacation, and not doing “parish work”. I am not sure that this is the best practice, especially considering that the men that are permanent Deacons are forbidden from wearing them. Which I don’t understand. After all, they are clerics, a seminarian is not.
I have no problem with the seminarians wearing clerical garb, in general. What I am not too sure about is the wearing of clerical garb like it is a “status symbol” when you are out shopping or at the movies or at a coffee shop with friends.
I did check with a friend who works in the Vocations department of my diocese, and there is no real “rule”, per se, except for the one that forbids permanent Deacons from wearing them.