Unfortunately this is an issue that has cropped it within the latest update for Acrobat/Reader 11.0.3. You can hide the message bar that appears by clicking the icon on the left of the message bar and if you're familiar with working with registry settings can follow the instructions provided in the version 11.0.3 release notes to disable this message.
Unfortunately this is not an issue with Adobe Reader. I don’t even have Reader installed. It’s a new issue with Acrobat XI.
Yes, that’s what I said. The problem is in both Acrobat and Reader 11.0.3. Here is a blog entry with a bit more detail:
Adobe Reader and Acrobat 11.0.3 update and signature field detection <http://blogs.adobe.com/acrobat/adobe-reader-and-acrobat-11-0-3-update-and-signature-field- detection/