first offer!

I got an email offer for a postdoc position (the formal letter will take a few weeks)! I want to cross out the $$ and hang it up on my door as was the custom in undergrad, but sadly nobody does that here. Also, I have no idea how to respond. The email was a bit strange, actually, and said: "Sorry it took me so long to get back to you. I'll start making a formal offer letter for you. The salary is $$." It didn't ask or imply any questions of me so it's unclear what I would include in a response except "Thanks. I'll wait for your letter." Help?