Business Reply Mail?

Hi!
I am trying to mail in a donation to the Humane Society, but through a Business Reply Mail...
1) On the top right corner, you can see a little square box with the text "No Postage Necessary If Mailed In The United States," what does this mean?
2) On the top left corner, it states "Your First-Class Stamp On The Envelope Is Another Gift To The Animals," what does this mean?
Please Help, Thanks!
Answers:
no postage necessary means that if it is sent in the us, you do not need postage (the company will pay for it)
also if you stamp it, it will be a gift to them because they will not have to pay for the postage