How is rent unpaid calculated for a sec 8 notice?

{Mod - this post moved from another active thread}

I to am in a similar situation and need to serve a Sec 8 notice on my tenant for non-payment of rent. A question that I don't think has been answered yet is do we need some sort of proof that the Sec 8 notice was served? Either recorded delivery or signature from the tenant and what if they refuse to sign?