It's doable in Exchange 2010 using disclaimers. This is a native thing. But it does just add it to the bottom of the email, not underneath the top reply.
This is one of our transport rules:
This adds the signature to all New emails, but replies or forwards don't get the signature added.
Apply Rule to messages from users that are 'Inside the organization' and when the sender's 'customattribute1:staff'
'append' '<div style="font-family: Calibri" style="border-top: solid 1px #000; border-bottom: solid 1px #000;">
<table style="width: 100%;" cellspacing="0" cellpadding="0" border="0"><tr><td><a href="http://www.crickhowell-hs.powys.sch.uk"><img src="https://folders.crickhowell-hs.powys.sch.uk/style/logo-black.png" alt="Crickhowell High School" style="border: 0;" /></a></td><td style="text-align: right"><img src="https://folders.crickhowell-hs.powys.sch.uk/style/dragon.png" /></td></tr></table>
Email: <a href="mailto%%Email%%">%%Email%%</a><br />
Tel: 01873 813500<br />
Fax: 01873 813550
</div>' and fall-back to 'wrap' if unable to apply.
except when the Subject field contains 'RE:' or 'FW:' or 'FWD:'
or except when the Subject or message body contains 'https://folders.crickhowell-hs.powys.sch.uk/style/logo-black.png'
or except if the message type is 'Automatic reply'
We also add an external disclaimer to all emails going to external contacts:
This adds the disclaimer to any email sent outside if it hasn't already been disclaimed and it's not an Automatic Reply (Out of Office Reply)
Apply rule to messages from users that are 'Inside the organization' and send to users that are 'Outside the organization'
'append' '<div style="color: gray; font-family: Calibri, Tahoma;"><p>This email and any attachments to it may be confidential and are intended solely for the use of the individual to whom it is addressed. Any views or opinions expressed are solely those of the author and do not necessarily represent those of Crickhowell High School or Powys County Council.
If you are not the intended recipient of this email, you must neither take any action based upon its contents, nor copy or show it to anyone.
Please contact the sender if you believe you have received this email in error.
</p></div>' and fallback to 'wrap' if unable to apply
except when the subject field or message body matches 'any attachments to it may be confidential and are intended solely for the use of the individual' or except if the message type is 'Automatic reply'