Purpose of "air mail" stickers

I notice that a lot of people ask senders to use “air mail” stickers. Can someone explain this? Does mail these days travel across continents in any way other than by air? I don’t know where I would even get these. I don’t believe the postal service offers them. Will the US Postal Service take my direction on what form of transport they use to get my postcard to its destination? I do understand that 100 years ago when planes were new, this might have been a “thing”. But now?

Any insights into this are much appreciated.

8 posts were merged into an existing topic: Air mail stickers

I moved your topic to the already existing topic linked earlier. We try to merge threads about the same topic to keep the forum as uncluttered as possible.