There is no rule.
Customs appear to have followed personal preference.
For example, pictures of Presbyterian ministers from the late 19th century reveal that some wore the typical suit and tie of the day while others wore a distinctive clerical collar. Q. I want to believe , but I constantly have doubts about faith and God. So if you want to believe, feel free to go ahead and do the things believers do. Read your Bible day by day, ready to hear what our Lord says to you from the text, and ready to put it into practice. Participate in a small group with people who will challenge and encourage you in a life that follows Jesus.