Hi,
today I've done a excursion to Exchange 2010 because I was asked, how you can implement a global signature in Exchange 2010.
Go to the "Organisation Configuration", select "Hub Transport" and choose "Transport Rules"
There you can add a new transport rule:
In the Conditions-Window you can select, that this rule applies to messages which will be send to users outside your organisation.
In the Actions-Window select "disclaimer" and add your text
The next windows you can accept by clicking on "Next" or you can define some exceptions for this rule.
That's it