Count the NT Workgroups that the current user is a member of.

Syntax
      IFMEMBER [options] WorkGroup [ WorkGroup2 WorkGroup3...]

Options:
        /verbose or /v   : print all matches.
        /list    or /l   : print all groups user is a member of

The %ERRORLEVEL% return code shows how many of the listed workgroups the currently logged-in user is a member of.

Examples

IFMEMBER /v /l "MyDomain\Administrators"
IF ERRORLEVEL 1 echo This user is an Administrator

Notice that the syntax here is the opposite to normal in that
%ERRORLEVEL% = 1 = Success
with most other NT commands %ERRORLEVEL% = 1 = Fail/Error

The best way to utilise IFMEMBER is through conditional execution...

IFMEMBER Administrators || ECHO Error is 1 so [%Username%] is in Admin_WG

IFMEMBER Administrators && ECHO Error is 0 so [%Username%] is NOT in Admin_WG