Looking for Sample Engagement Letters:

Thank you so much for reading my forum post!  I am working on creating an Engagement Letter template to enhance our current Internal Audit process.  The letter will be used to set clear expectations regarding the engagement/audit (e.g., client's responsibilities vs. Internal Audit's responsibilities) and seek agreement.  I'm looking for sample Engagement Letters and appreciate anyone that is willing to help.

I'm also curios, if you have an Engagement Letter do you have the client sign it and why?