[gbuk2013]

I don't own a TV. :) I do watch some movies now and again though, especially when flying long haul but I never had one that mentioned those. Off the top of my head I can only think of 24 as a candidate but I never watched that.

[mistermann]

Anyone who's spent any significant amount of time in political threads in reddit (just for example) would know those acronyms.

[Sacho]

I think it's not a matter of knowing the acronyms but rather using them in your writing. Even though I'm aware of POTUS, I would simply write "The President" or "The US President" - it comes much more natural, from all the times its been used in local media to refer to our own/foreign presidents. Same reasoning for the US Supreme Court.