Other than a date stamp or "Restricted..." warning stamped onto them, there is no physical difference between a pre-ban and a post-ban mag. The difference is LEGAL. Mags manufactured after 9/13/94 are illegal for normal persons to possess, under the federal "assault weapons" laws (which will be expiring in a week).
Regarding the magazine portion of the law, the burden of proof that a mag is restricted is on the government. Note that this is very different from the firearm portion. If your mag has a date of 09/94 or earlier, or has no markings (most "preban" mags were not marked), then it is legal to possess (i.e., "preban"). If the mag has a date stamping of 10/94 or later, or has a "Restricted to LEO/Gov't/Military/Export Use Only" marking, then it is illegal to possess unless you are one of those persons (i.e., "postban").
Your mags are legal.
-Troy