role is a name of the server role. It is a sysname.
login is an optional name of the logged in user. It is a sysname. If you don't specify, the current user login account is used.
Return type of IS_SRVROLEMEMBER is an integer. It returns 1 when login is a member of role, 0 when login is not a member of role and NULL when role or login is not valid.
Examples of IS_SRVROLEMEMBER Function :