Did 'show interface' not help you??
http://www.cisco.com/en/US/docs/security/fwsm/fwsm32/command/reference/s3.html#wp2754219
"Usage Guidelines
You can use this command to display the status of interfaces. You can specify the ID (as either the VLAN or the mapped name) or the name of the interface.
The dropped packets statistic in the display shows a record of those packets that arrived on the interface, but were not destined for the FWSM. These packets include traffic flooded by the switch, multicast and broadcast traffic (unless the FWSM is configured to relay those) and packets that fail sanity checks such as incorrect IP length versus Layer 2 length or checksums. This counter does not record packets dropped by the security policy. "
