I always use 312-836-7000, which is the CTA's customer service number. It stuck in my head from years of bus commuting in Chicago. It most recently worked for me as a loyalty card at a Safeway in Mountain View, so I'm apparently not the only one with this number stuck in their head. But not enough people know it for it to be flagged. (Never tried it when I lived in Chicago, interestingly. There it might be more widespread.)