It's been far too long since my second child was born, but we finally booked the tattoo appointment. As I did with my first, I got a tattoo with the latitude, longitude, date, and time of his birth. Finding the right font is hard - I wanted something that doesn't completely contrast with the existing tattoo, but was still distinct. Eventually, this is what I ended up putting together.
41°56'11"N 87°39'03"W 2017-05-29T20:10