what should i engrave???

i got the girls tiffany charm bracelets and one of the charms is a heart. i want to engrave it. but what do i put on it?? i know the front i wanna put their name, but do i do there whole name, just inital or the 3 intials with the one bigger in the middle?? and what do i put on the back?? thank you? the date? halp please!!!!


thanks!