Shubert Alley Cat said: "Can you earn audience rewards points if you purchase tickets at the box office?"
There is a list of theaters on their website, under Terms & Conditions at the bottom of the page, where you can find out which theaters will add your AR number to the purchase order right at the box office. Here you go:
Earning ShowPoints for Box Office Purchases. Select box office locations allow members to earn points for purchases made at the box office. See below for a list of participating box offices. In order to receive points at participating box offices, please be sure to bring your Audience Rewards number to the box office and provide to box office staff when making your purchase.
- Ambassador Theatre - New York, NY
- Belasco Theatre - New York, NY
- Bernard B. Jacobs Theatre - New York, NY
- Booth Theatre - New York, NY
- Broadhurst Theatre - New York, NY
- Broadway Theatre - New York, NY
- Ethel Barrymore Theatre - New York, NY
- Gerald Schoenfeld - New York, NY
- Imperial Theatre - New York, NY
- James Earl Jones Theatre - New York, NY
- John Golden Theatre - New York, NY
- Longacre Theatre - New York, NY
- Lyceum Theatre - New York, NY
- Majestic Theatre - New York, NY
- Music Box Theatre - New York, NY
- Shubert Theatre - New York, NY
- Winter Garden Theatre - New York, NY
You can also call them (866) 313-9635 weekdays between 10a-5p for more information, or to make sure that the theater(s) in which you're interested are still participating. Given that some of the stuff on their site (i.e. the defunct Trivia questions) is out of date, you might want to double-check.