Using cash for small purchases like a cup of coffee, gum and other items is a good indication that a person is trying to pass for normal without leaving the kind of paper trail created using a debit or credit card for small purchases.
The most recent update asks coffee shop owners, baristas and other customer-service specialists to be on the lookout for the enemy who walks among us (who evidently has been reanimated from the graves of the 1950s Red Scare era of blacklisting and Communist-baiting or the KGB's constant witch hunt for capitalist sympathizers or people who resent being witch-hunted for their political beliefs).
No one objects to the FBI or any other law enforcement agency keeping an eye out for terrorists. Trying to get everyone involved in such a silly, time-wasting way to manufacture suspicion and false accusations is not the way to do it.
Not only does it waste time by identifying everyone as a potential suspect, it erodes what alertness or willingness to cooperate members of the public may have by crying wolf over and over until, the next time a real wolf does show up, it's more likely to get a cup of coffee and pat on the back than a suspicious look-over by a hard-eyed barista.