I have never seen one either, but I don't use Google search anymore.

Perhaps you don't use it either?

I've never seen too, and I use only Google search (though not on Android).

I think they only appear if you're using Google Search from Mobile.

I use google search and chrome on Android and haven't seen one either. I don't see the AMP icon when I search for 'git tips'. Maybe it's US only for now.