In order to implement Gmail-style Undo labels integrated into the UI, you'll have to store more information about the operation. This can be done by getting the current ZODB transaction and adding a note to it. This information is later available in the description attribute of the transaction entry in the transaction history log.

To add a transaction description

import transaction
transaction.get().note('label-something-done')

To get the translated transaction description from the transaction history log

def getLastTransactionNote(context=None):
    umgr = zope.component.getUtility(IUndo, context=context)
    transactions = umgr.getTransactions(context=context)
    last_transaction = transactions[0]
    return _(last_transaction['description'])

Of course, you'll probably want to get the transaction id as well, to be able to do an undo. To get more info about this read the zope.app.undo.interfaces.IUndo interface description.