Think something positive and smile at Baby, even if what you're smiling about is that you feel so damn lucky that you are not at Baby's beck and call 7x24 and you have to guess what Baby wants from Baby's crying, and that you are not the one who is dragging their sorry butt into the office for a full day's work after a round of diaper changing at 3 AM :)
You don't have to say anything - smiling at Baby is enough. If you really want to say something, ask one of the parents "What's Baby's name?" And if Baby's name is say "Lisa", you say "Hello, Lisa. Good to see you!" and then you do whatever you want from this point - stay and chat a little bit or take your leave to get back to your desk - Whatever you feel comfortable with doing next. It's not complicated.
There are 50 reasons why babies cry, none of which may have anything with you unless Baby caught you giving it the Death Stare. At this stage of their lives, crying is pretty much the only method they have to communicate with #1, which is their mom. If they aren't crying, then that's because they're having their beauty sleep. If they're gurgling, this means that they aren't hungry and they don't need #1 to hold them. Again, if you are not giving Baby the Death Stare and baby happens to cry when you merely look at it, you're probably flattering yourself if you think that you have anything to do with their crying :) Compared to "#1, I WANT YOU TO HOLD ME. RIGHT NOW!" or "I'M ABOUT TO POOP, AND IT HURTS!", you're probably not even worth a belch to Baby :) Yes, I wrote it in capitals and writing in capitals are the equivalent of screaming. Well, Baby crying is the equivalent of screaming. When was the last time that Baby wanted something and did not scream for it? Because when Baby wants something, Baby wants it all and Baby wants it now :)
Personally, because I have a great relationship with my bosses, I'd look at Baby and ask one of the parents "Is Baby our new CEO? Damn, they're getting younger and younger and smarter and smarter. I can't take it anymore, I am quitting!" ) At times, I have been guilty of being belligerent and I have said point-blank to the father "She looks a lot smarter and prettier than you!" :)
Follow-up comment from @BigHomie "Death scares don't scare real infants, trust me"
First, they'd have to be old enough to recognize faces. Second, they'd have to be old enough to recognize expressions on faces :)