Notice period buy out is in most companies treated as part of " Recruitment Expenses". As it is to on- board talent on fast tract it is given treatment as TA Expenses and the budget is taken under Hiring Managers Budget in many big companies and it is most appropriate also.
Such reimbursements are to be done with care as in many cases it is paid along with first month salary and once received the Talent quits or leave job abruptly. Have a clear documentation that the reimbursement will be done in 3 parts / instalments one along with 2nd month salary, next in 4th month salary and last in 6th month salary. If some one leaves the service within 1 year, the said reimbursement will be deducted upto 75% etc.
From India, Chennai