Exchange Server 5.5 & Web Outlook Access

Just migrated 150 users to Exchange 5.5
I have 30 users offsite using OWA as thier main email client. The users offsite want to put signatures on the outgoing email. Am I missing something or is this not supported as "Signature Picker" is in Outlook 2000 or any other email client? Cirumstances dictate that they use OWA. The old Webmail client they used before supported this. So, I can already hear the cries. Missing something? Third party add-in?
Any feedback is much appreciated

Thanks