In addition to knowing where the sticker is ahead of time, it is also a good idea to bring a printout of the airline's written policy for child restraints, printed from their website, with the airline name or logo on it.
I had an experience when our DS was 4 mos old and a flight attendant tried to tell us we could not install his carseat rear-facing unless we were in the bulkhead seat. It was an idiotic thing all the way around because carseats aren't even allowed on the bulkhead row. And the airline's own policy specifies rear-facing until age 1 and 20 lbs. I did not have the copy of the policy with me and this uninformed attendant had the power to prevent us from installing it correctly. I was not going to intall it FF for a 4-mo, and I thought we were going to have to refuse the flight because of him and get someone higher up on the phone to make arrangements for us on the next flight. Fortunately, another flight attendant stepped in and corrected him. On our return flight I carried the printed policy with me in case we had trouble again. I also formally complained to the airline and received a written apology and statement that the "training issue would be addressed". From now on I tell everyone I know who is flying with a carseat to know where the sticker is, and have a printout of the policy in their pocket, with the installation details highlighted.