When we travel my husband usually carries all of our passports. However, when we go through checkpoints everyone needs to have his or her own passport and ticket.  Since all of our passports look exactly the same from the outside I used washi tape to differentiate them to make passing them out a little easier. I left my husband’s blank, I taped mine near the top and my daughter’s near the bottom.  We happened to have different patterns of tape but if you don’t just vary the position and it will work just as well.  I wish you happy travels and fast-moving customs lines!