Hi,
HRM in US means you have to registered as certified HR Professional from recognised institute in USA. These institutes are listed on website.
You have to be conversent with the HR practices in the USA because unlike Indian HR USA has diffrent set of business organizantion priorities and their modus operandi or we can say modules are different. For example their HR professional are specialist in any of the one subjects with latest software knowledge for BPR, SAP-HR ,payroll etc. some psychometric test in case of recruitments, Most of organizations used point rating methods for Job Evaluations and many used Hay's three Point factor job evaluation which required proper training to evaluate ratings for each job and job families as wells job ladder and market pricing as well as Western specially US salay scale structure consist of minimum-mid-maximum. grading structure and market pricing etc.
You have to under go training and exposure for US MNC to be acquinted with the HR practices in USA.
Regards
Sawant