A handful of tags have emerged to identify the country to which the question pertains. We've got uk, usa, and united-states.
Should we be using abbreviations (UK, USA) or full names (United-States, United-Kingdom) for our country tags? It would be best to standardize on one or the other now, and to set up tag synonyms so that we don't have duplicated tags like in the case of usa and united-states.
I recommend following what Travel does. They use the usual name of the country, with a few synonyms to accommodate common names like united-states → usa and korea → south-korea. I recommend this because:
Consistency is good.
It's a tried-and-tested naming scheme.
The tags are perfectly comprehensible when you read them, and it's immediately obvious what the tag for a country is.
Abbreviations suck. What's the two-letter abbreviation for Germany? Where's ch?
Given that this site is US-centric due to the partnership with the USPTO, there should probably not be a US tag. There is international to discuss cross-country issues such as PCT applications (which may warrant their own tag).
WIPO (World Intellectual Property Organization) has a list of country codes that they use. Most are similar or identical to TLDs and common sense, but it may make sense to consider their codes given that the same codes are used by the patent offices themselves. Side note: WIPO is in charge of settings patent data standards that are used by the EPO and (to a large extent) the US.