The type of call signs that you referenced are referred to as 1x2 (one by two) call signs in the USA. Due to the limited number of such call signs and their historical significance, these are the most sought after in the USA.
But 1x2 call signs are not unique to the USA. Consider the well publicized (but commonly misunderstood) G5RV antenna, named after the UK 1x2 call sign holder that invented it. The call is currently held by a UK club in commemoration.
An even more rare call is a 2x0 call sign. A popular example of this was King Hussein of Jordan, JY1. While he could obviously obtain any Jordanian call sign, he was known for his personable on the air conversations despite his political standing.
In the USA, hams may apply for a 1x1 call sign that may be used for special events for a limited time. The call is then recycled for future applicants.
Note that the call sign prefix (the part before, or including, the number) is assigned by the ITU. A listing may be found here