Does anyone know of a widely accepted icon (such as a "quetion mark" for help) for "contact us" or "fed-back", if such exist?

An enveloppe is often used for a "contact us" icon. For a feedback, I don't know.

Thank you.
There will be a "Contact Us" link on the main menu, which will lead to a form. What I was looking to do was to create an "auxiliary" icon for feedback and/or comments specifically for the web site, not the business activities of the company.