The first thing you should do is NOT place your ClixSense affiliate link on the cards.
Instead, go to TinyUrl dot com and get a free short redirect, use that for your ClixSense affiliate link.
Yes, some places it is against the law to leave flyers/promo items. However, there are places that
usually do not care such as laundry mats and post office bulletin boards and also some grocery stores
have bulletin boards.
When in doubt, simply ask the institution if it is ok to leave your card/cards.