From "SQL Server DMV Starter Pack" by Louis Davidson and Tim Ford.
Calculates the signal and resource waits as a percentage of overall wait time.
As Signal waits are the time waiting for the CPU to service a thread, if the signal wait time is about 10-15% then your CPU may be under pressure.
These wait stats are cumulative since SQL started, so will not give a result that reflects CPU loading over the previous few minutes. You can use DBCC to clear the wait stats and get a better snapshot of the current CPU loading state.
DBCC SQLPERF('sys.dm_os_wait_stats', CLEAR)
You can run this in SQL Script Manager using the 'Clear Wait Statistics' scripts