If you pick up the business card of any professional Mistress, it is your own responsibility what you decide to do with it, where you decide to keep it and who you let see it.
If your wife (husband/partner/relative/other) finds the business card of a professional Mistress in your wallet (purse/pocket/whatever) which you have picked up upon secretly visiting a dungeon or have picked up at one of the BDSM venues which have little piles of them on the bar (reception/other) and she (he/it) then decides to phone the number on the card to ask (anonymously) if the Mistress has recently visited the said venue (city/county/area/other), the Mistress will have no reason not to tell the truth.
Secrets are not often good, lies are certainly never good, both are a persons own responsibility and have nothing to do with the Mistress. It is not their affair.
Remember this if you decide to pick up a business card which profiles any form of BDSM professional or service.
Stupidity is its own punishment.