4. Already on it...just need to get it there without the wife noticing!
Being a new parent, here are my suggestions for possible places...

1. on the back of baby carrier. It faces front while the baby is little.

2. on the stroller just above the step before the fabric...usually this area is plastic.

Another idea is get an Xmark patch from Rocky and sew it on the front of your (Baby Bjorn-like) baby carrier...Baby Bjorn...which I highly recommend. It's truly worth the money. IMHO, nothing better than wearing your baby.

Cheers