You could also do it another way - find out the uuid of the disk by issuing the command when that usb is inserted first time (the objective is to find out the uuid) by using vol_id
vol_id - probe filesystem type and read label and uuid
vol_id [--export] [--type] [--label] [--label-raw] [--uuid]
[--offset=bytes] [--debug] [--help]
vol_id is usually called from a udev rule, to provide udev with the
filesystem type, the label and the
uuid of a volume. It supports most of
filesystem formats and detects various raid setups to prevent the
recognition of raid members as a
volume with a filesystem.
Print all values in key/value format to import them into
Print the filesystem type.
Print the safe version of volume label suitable for use as
Print the raw volume label.
Print the uuid of a volume.
Skip detection of raid metadata.
Probe for all types and print all matches.
Start probing at the given offset, instead of the beginning of
the volume. The offset value is
specified in bytes.
Print debug messages to stderr.
Set the syslog priority.
vol_id will only return successful if the value asked for is
not empty. All trailing whitespace
will be removed, spaces replaced by
underscore and slashes
Then it's a matter of checking the vol_id once you have the value for that disk...