Look for a torch or diamond logo on your lock.
Visit http://www.tsa.gov/travelers/airtravel/assistant/locks.shtm to see if the logos on the lock match. If they match what's shown on the Web site, the lock is TSA approved.
Inspect the lock for other logos. If there is a different logo, your lock may still be TSA approved if a new company has partnered with the TSA. Verify the logo by visiting http://www.tsa.gov/travelers/airtravel/assistant/locks.shtm to see if the logo matches one of the TSA partnering companies. If it matches, it is approved.
If your lock has no logo on it, it is not TSA approved.