In theory, if a commercial giant like Coca-Cola approached a bankrupt country such as Chad or Ethiopia, and offered a large sum of American currency to them if they added the Coca-Cola logo to their flag, could they do it?
Are there any United Nations rules stating what can and can’t be done?
I know that if this happenned in real life there would probably be some sort of uproar, but is it a theoretical possibility?
I don’t think that policing flags is the UN’s number one goal. I really don’t think that anything would happen to them.
Laurent Kabila’s “new & improved” Congo, aka “the country formerly known as Zaire”, has lately been using a flag bearing the image of Simba the Lion from Disney’s The Lion King. This was done on Kabila’s orders and not any behest from Disney Corp. I’m not sure it is recognized internationally but last I heard, it was being flown in their capitol city etc.
As far as advertising on a flag I suppose it is theoretically possible, but it seems to me that a nation risks withering international scorn by selling out its primary national symbol for the glorification of something along the lines of American sugar water.
It also seems to me that very little is in it for the corporation as far as a cost/return basis re: advertising visibility. (Can anyone describe to me, without checking, Chad’s flag? I didn’t think so; it’s because you never see it flying anywhere.)
And would a company really want to associate themselves so intimately with some bankrupt third-world hellhole? Certainly most of the payola would tend to concentrate itself in a very few pockets, rather than enriching the nation as a whole. Then you’re left with a corporate logo representing an impoverished nation. I doubt any business would want to risk the PR questions of “why is the country with your logo on its flag so dirty / poor / illiterate / corrupt etc.”
Yellow, blue, and red (not sure about the red) horizontal stripes. 
In Romania.
BTW, get your flag trivia here: http://www.crwflags.com/fotw/flags
The Flag of Chad? Sure can. It’s a field of orange with a little over 1,100 symmetrically laid out squares, some with torn corners, many with dimples 
Cartooniverse
The UN?
Most country’s flags are determined by the dictator, or “President”-for-life.
I never heard this.
BTW, the official flag of the Democratic Republic of the Congo is a blue field with six yellow stars going vertically on the left-hand side and one large yellow star in the center.
The flag of Mozambique has an AK-47 on it. As far as I know they never got any money from the Kalashnikov people.
Libya’s seems to scream “space for rent”. Maybe somebody should suggest it to them …
Yeah, here’s Libya’s flag (enlarged to show detail ).