The tattoo is in an area that is not managed by the BES Client to ensure that it will remain intact regardless of the state of the BES client. See also "Tattoo custom completion check.bat" relevance snippet which checks the tattoo.
//This goes at the end of the action script in the task. The next line assumes that the exit code of the batch file, executable, or whatever was last executed returns 0 or 3010 on success.
// Task should fail now if exit code is not 0 or 3010. Exit code should also be returned in report for action instance.
continue if {exit code of action = 0 or exit code of action = 3010}
// Write a tattoo to indicate completion. The tattoo is in an area that is not managed by the BES Client to ensure that it will remain intact regardless of the state of the BES client.
regset "[HKEY_LOCAL_MACHINE\SOFTWARE\BSHSI\BigFixCompleted]" "UniqueNameHere"=dword:00000001