So, here's a short-but-sweet difference, suggested by Not From Around Here:
In BrE, this is bunting. In AmE, I'd call it a string of pennants. This picture comes from a panicky article in the Telegraph:
Royal wedding party 'crisis' as bunting stocks run low
Now, I suspect that some AmE speakers will know this sense of bunting. The most recent edition of the American Heritage Dictionary includes it as 'Strips of cloth or material usually in the colors of the national flag, used especially as drapery or streamers for festive decoration.' But, judging from comments/questions I've heard in the cacophony of American voices commenting/asking about the wedding, I don't think it's widespread in AmE at this point. Compare the results for a search for bunting on Amazon.com and Amazon.co.uk, and you'll see what I mean.
Growing up in the US, I knew a decorative sense of bunting, but it was limited to this stuff (from Amazon.com):
The original meaning of bunting refers to the type of material that flags are made from, and then, by extension, it refers to things that are made out of that material. But the understanding of it particularly as 'strings of (decorative) flags' is ubiquitous in the UK. This sense in particular is not recorded in the OED (2nd edn, 1989), but I think it'll need to be in the next one, as I think it's the sense that most BrE speakers know--regardless of whether they know the more general 'material' sense.
There are, of course, other (unrelated) meanings for bunting. It's a kind of bird, for example. And, apparently, there's a dialectal difference here. In English generally, it applies to birds from 'Emberizinæ, a sub-family of Fringillidæ', and the particular species are generally called by compound names like rice bunting and corn bunting. But in AmE it's also '[a]pplied by extension to any bird of the bunting subfamily, and to similar birds of other families' (OED).
An AmE sense is related to baseball. To bunt is 'to stop the ball with the bat, without swinging the bat'. For more on why you'd want to do that, see Wikipedia. This comes from an older BrE-dialectal word meaning 'to strike' (OED notes it in Wiltshire and Sussex).
Then there are the baby senses. OED has "A term of endearment: in ‘baby bunting’, the meaning (if there be any at all) may possibly be as in Jamieson's ‘buntin, short and thick, as a buntin brat, a plump child’". Now, I only know this from a nursery rhyme that I only know from my time in the UK. The AHD doesn't record this one, so I'm going to call it BrE.
But AmE has bunting as 'A snug-fitting, hooded sleeping bag of heavy material for infants.' Like this one by Gap (from a UK site, but I'm assuming the name was imported along with the item):
These days, most things that are called baby buntings on US sites are indistinguishable from snow suits (which is what they'd also be called in BrE), in that they have legs, rather than a 'bag' at the bottom. The simple reason for this is that now all babies have to be strapped into car seats and (AmE) strollers/(BrE) push-chairs, with one of those straps going between the legs.
AHD gives the etymology as 'Perhaps from Scots buntin, plump, short.' So, we've got two baby-related senses (neither of which I caught in the big baby-related post), both supposedly coming from the same source, but mostly not shared between AmE and at least mainstream English-English. Scottish readers--do you use any buntings in this sense?
Bringing this back to the wedding: hanging bunting is a prime way to show involvement in the big day. So, it hangs in shop windows and will be strung around wedding street parties. But I'm not in the best place to show you BuntingFest 2011, as I live in what may be the most apathetic-about-that-wedding part of the country. While Not From Around Here estimates that one in three shops in her town are decorated for the wedding, in Brighton/Hove/Portslade yesterday (I got around), it looked more like one in ten. And even then, it was often very half-hearted (say, a free-with-purchase flag or poster from a tabloid newspaper). Most of the (BrE) charity shops/(AmE) thrift stores have wedding gowns in their windows, but people I know are buying the cheap ones and wearing them with zombie make-up to go on (BrE) pub crawls. I've heard of no earnest street parties in Brighton and my Twitter feed is full of locals resenting the cost to the taxpayer at a time when the government is drastically cutting funding to just about everything else. (Some people counter that the wedding generates millions in UK spending, but we must remember that this is at the expense of many times that much in lost productivity because of the extra holiday.) The one sincere party I know of happened at my daughter's preschool on Thursday, where girls were dressed as princesses or brides and boys as princes or grooms. And all I can say is: I'm so glad Thursday is Grover's day off. (It's not the monarchism per se that bothered me, but the encouraging girls to dress up as princesses and brides. I would like to encourage her to dress up as an astronaut or a dragon or anything that isn't giving her the message that looking pretty is all that girls are supposed to do.) Though I've had to swear an oath of allegiance to the Queen and her successors, I can't imagine that the television will be on anything but Zingzillas tomorrow. (And if you don't know what Zingzillas is, you can count your lucky stars that you don't have the theme song going through your head right now. Make it stop! Please!!!)
And that's me doing a short and simple, dash-it-off post. Oh wait, it's 3am. I'm never going to be any good at this, am I?