When I forward an email the font changes...

One of the users here has an issue with her Outlook 2k3 changing the font of a signature to something illegible. This only occurs when forwarding an email from a specific contact. When the email is recieved by this person, his signature is completely fine. But when the user forwards that email, the signature from the previous email changes. I selected the signature to check to see if the font changed, but it did not, its the same font and size. However the signature now looks like Jer@%%%!! etc. This only happens on her pc. I had her forward the email to me and when i open it and forward it to someone else, the font does not change. I tried using both Word and outlook for writing emails... rich text, plain text, html. All with the same results. Any ideas on what causes this?