If you were so upset about these women and discovered that they were eating treif that you didn’t take that issue up with your RAV but chose to ask your sheilah here? That bothers me, and indicates to me that you might not be honest and sincere.
Secondly, if you suspect that they are eating treif, you could easily stop at their table and cleverly say “oh, i didn’t know that this store was kosher, who gives the hechser here?”. That would be the nicest and most polite way of bringing it to their attention without snooping behind their backs, asking the non-jew or non-frum jew who works the counter or giving tochacha because you feel you are better then them. I’m sorry if I offend you but that is what the tone of your post sounds like.
The appropriate thing to do if you think they are eating treif is take it to your RAV and ask him if you should say something, or if you should ask the guy behind the counter to let them know that it is not a Kosher store. If he says you should approach them, he will probably ask you if you know for sure that they bought the food there and did not bring it from home and just buy coffee. IF you know for sure that they bought it there, then maybe the best thing to do with the RAV’s ok, is to do as I suggested and act surprise and say “I didn’t know this store was kosher, who gives the hasgacha here?”. This will cause the least amount of embarrassment for them if said in the proper tone and not in a sarcastic manner. Or if they go at a regular time, maybe the Rav himself can go in and just stop by and mention, “You probably didn’t realize, but this store is not one of the Kosher Starbucks.” This is also a way to minimize their embarrassment. There are ways of giving tochecha that doesn’t have to cause embarrassment and humiliation especially when someone is doing wrong b’shgagah and not purposely.