Great thread!
I've thought of this often, wondering how I can approach others. Alas, I've come to the conclusion that I will probably not say anything at all, except:
"oh what a beautiful baby/child/daughter/son."
Another adoptive parent once stated that they feel like they often put their child up for "display" and have dubbed their child as a "Guatemala Adoption Embassador" - i can see this happening.
It's partially because I'm a very private person, and partially because I've heard all kinds of stupid comments growing up (my family is Hispanic), but I will probably not respond as well as I should if another parent (whether an adoptive parent or not) came up to me and asked if my child was adopted.
So I more than likely will not say anything at all to another family. ..

__________________
Whether you turn to the right or to the left, your ears will hear a voice behind you, saying “this is the way; walk in it.”
Isaiah 30:21
December 2003 - Decided to adopt from Guatemala
10/15/05 Began
Baby Girl
2/23 "chiquitita" Referral

(dob 1/30)
April to August: Stuck in PGN

8/29 Pink
9/7 Embassy Appointment
9/10 Home!
Baby Boy
3/22 "chiquitito" Referral

(dob 2/25)
May to Aug: Stuck in PGN

8/23: Pink
9/7 Embassy Appointment
9/10 Home!