Yours sincerely is a standard British form while Sincerely yours is a US variant.
Nevertheless, Sincerely yours is not that common as you think.
In formal letter, most Americans still DON'T use Sincerely yours.
Secondly, Sincerely yours contains a meaning of "intimacy" and to UK people that meaning has no difference from "All yours". Thus, "Sincerely yours" is avoided to be used in most of the FORMAL situations.
And, it is worse that "Sincerely yours" is considered as incorrect in British English.
Please think twice before using this phrase or you may face difficult circumstances.
http://zhidao.baidu.com/question/44334753.html?si=2
Nevertheless, Sincerely yours is not that common as you think.
In formal letter, most Americans still DON'T use Sincerely yours.
Secondly, Sincerely yours contains a meaning of "intimacy" and to UK people that meaning has no difference from "All yours". Thus, "Sincerely yours" is avoided to be used in most of the FORMAL situations.
And, it is worse that "Sincerely yours" is considered as incorrect in British English.
Please think twice before using this phrase or you may face difficult circumstances.
http://zhidao.baidu.com/question/44334753.html?si=2